diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -23,7 +23,7 @@
 
 To build and run a specific test in `tests/purs/passing/` or `tests/purs/failing/`, add test arguments like so:
 
-`stack test --fast --test-arguments="-p compiler/**1110.purs*"`
+`stack test --fast --test-arguments="-p 1110.purs"`
 
 This will run whatever test uses the example file `1110.purs`.
 
diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -93,7 +93,7 @@
 | [@pseudonom](https://github.com/pseudonom) | Eric Easley | [MIT license](http://opensource.org/licenses/MIT) |
 | [@quesebifurcan](https://github.com/quesebifurcan) | Fredrik Wallberg | [MIT license](http://opensource.org/licenses/MIT) |
 | [@rightfold](https://github.com/rightfold) | rightfold | [MIT license](https://opensource.org/licenses/MIT) |
-| [@rndnoise](https://github.com/rndnoise) | rndnoise | [MIT license](http://opensource.org/licenses/MIT) |
+| [@rndnoise](https://www.github.com/rndnoise) | rndnoise | [MIT license](http://opensource.org/licenses/MIT) |
 | [@robdaemon](https://github.com/robdaemon) | Robert Roland | [MIT license](http://opensource.org/licenses/MIT) |
 | [@RossMeikleham](https://github.com/RossMeikleham) | Ross Meikleham | [MIT license](http://opensource.org/licenses/MIT) |
 | [@Rufflewind](https://github.com/Rufflewind) | Phil Ruffwind | [MIT license](https://opensource.org/licenses/MIT) |
@@ -126,6 +126,7 @@
 | [@sloosch](https://github.com/sloosch) | Simon Looschen | [MIT license](http://opensource.org/licenses/MIT) |
 | [@rgrinberg](https://github.com/rgrinberg) | Rudi Grinberg | [MIT license](http://opensource.org/licenses/MIT) |
 | [@gabejohnson](https://github.com/gabejohnson) | Gabe Johnson | [MIT license](http://opensource.org/licenses/MIT) |
+| [@dariooddenino](https://github.com/dariooddenino) | Dario Oddenino | [MIT license](http://opensource.org/licenses/MIT) |
 
 ### Contributors using Modified Terms
 
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -20,7 +20,5 @@
 ## Help!
 
 - [#purescript @ FP Slack](https://functionalprogramming.slack.com/)
-- [PureScript Language Forum](https://purescript-users.ml/)
+- [PureScript Language Forum](https://discourse.purescript.org/)
 - [PureScript on StackOverflow](http://stackoverflow.com/questions/tagged/purescript)
-- [Google Group](https://groups.google.com/forum/#!forum/purescript)
-- [Gitter Channel](https://gitter.im/purescript/purescript?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
diff --git a/app/Command/Bundle.hs b/app/Command/Bundle.hs
--- a/app/Command/Bundle.hs
+++ b/app/Command/Bundle.hs
@@ -7,7 +7,6 @@
 module Command.Bundle (command) where
 
 import           Data.Traversable (for)
-import           Data.Monoid ((<>))
 import           Data.Aeson (encode)
 import           Data.Maybe (isNothing)
 import           Control.Applicative
@@ -21,8 +20,7 @@
 import           System.IO (stderr, hPutStr, hPutStrLn)
 import           System.IO.UTF8 (readUTF8File, writeUTF8File)
 import           System.Directory (createDirectoryIfMissing, getCurrentDirectory)
-import qualified Data.ByteString.Lazy as B
-import qualified Data.ByteString.UTF8 as BU8
+import qualified Data.ByteString.Lazy.UTF8 as LBU8
 import           Language.PureScript.Bundle
 import           Options.Applicative (Parser)
 import qualified Options.Applicative as Opts
@@ -124,6 +122,6 @@
             case sourcemap of
               Just sm -> do
                 writeUTF8File outputFile $ js ++ "\n//# sourceMappingURL=" ++ (takeFileName outputFile <.> "map") ++ "\n"
-                writeUTF8File (outputFile <.> "map") $ BU8.toString . B.toStrict . encode $ generate sm
+                writeUTF8File (outputFile <.> "map") $ LBU8.toString . encode $ generate sm
               Nothing -> writeUTF8File outputFile js
           Nothing -> putStrLn js
diff --git a/app/Command/Compile.hs b/app/Command/Compile.hs
--- a/app/Command/Compile.hs
+++ b/app/Command/Compile.hs
@@ -8,11 +8,9 @@
 
 import           Control.Applicative
 import           Control.Monad
-import           Control.Monad.Writer.Strict
 import qualified Data.Aeson as A
 import           Data.Bool (bool)
-import qualified Data.ByteString.Lazy as B
-import qualified Data.ByteString.UTF8 as BU8
+import qualified Data.ByteString.Lazy.UTF8 as LBU8
 import           Data.List (intercalate)
 import qualified Data.Map as M
 import qualified Data.Set as S
@@ -52,7 +50,7 @@
       exitFailure
     Right _ -> return ()
 printWarningsAndErrors verbose True warnings errors = do
-  hPutStrLn stderr . BU8.toString . B.toStrict . A.encode $
+  hPutStrLn stderr . LBU8.toString . A.encode $
     JSONResult (toJSONErrors verbose P.Warning warnings)
                (either (toJSONErrors verbose P.Error) (const []) errors)
   either (const exitFailure) (const (return ())) errors
@@ -137,22 +135,15 @@
       <> " The default target is 'js', but if this option is used only the targets specified will be used."
       )
 
-targets :: M.Map String P.CodegenTarget
-targets = M.fromList
-  [ ("js", P.JS)
-  , ("sourcemaps", P.JSSourceMap)
-  , ("corefn", P.CoreFn)
-  ]
-
 targetsMessage :: String
-targetsMessage = "Accepted codegen targets are '" <> intercalate "', '" (M.keys targets) <> "'."
+targetsMessage = "Accepted codegen targets are '" <> intercalate "', '" (M.keys P.codegenTargets) <> "'."
 
 targetParser :: Opts.ReadM [P.CodegenTarget]
 targetParser =
   Opts.str >>= \s ->
     for (T.split (== ',') s)
       $ maybe (Opts.readerError targetsMessage) pure
-      . flip M.lookup targets
+      . flip M.lookup P.codegenTargets
       . T.unpack
       . T.strip
 
diff --git a/app/Command/Hierarchy.hs b/app/Command/Hierarchy.hs
--- a/app/Command/Hierarchy.hs
+++ b/app/Command/Hierarchy.hs
@@ -22,7 +22,6 @@
 
 import           Control.Applicative (optional)
 import           Data.Foldable (for_)
-import           Data.Monoid ((<>))
 import qualified Data.Text as T
 import qualified Data.Text.IO as T
 import           Options.Applicative (Parser)
diff --git a/app/Command/Publish.hs b/app/Command/Publish.hs
--- a/app/Command/Publish.hs
+++ b/app/Command/Publish.hs
@@ -5,7 +5,6 @@
 import           Control.Monad.IO.Class (liftIO)
 import qualified Data.Aeson as A
 import qualified Data.ByteString.Lazy.Char8 as BL
-import           Data.Monoid ((<>))
 import           Data.Time.Clock (getCurrentTime)
 import           Data.Version (Version(..))
 import           Language.PureScript.Publish
diff --git a/app/Command/REPL.hs b/app/Command/REPL.hs
--- a/app/Command/REPL.hs
+++ b/app/Command/REPL.hs
@@ -31,7 +31,6 @@
 import           Control.Monad.Trans.Reader (ReaderT, runReaderT)
 import           Data.FileEmbed (embedStringFile)
 import           Data.Foldable (for_)
-import           Data.Monoid ((<>))
 import           Data.String (IsString(..))
 import           Data.Text (Text, unpack)
 import           Data.Traversable (for)
@@ -319,19 +318,19 @@
           unless (supportModuleIsDefined (map snd modules)) . liftIO $ do
             putStr supportModuleMessage
             exitFailure
-          (externs, env) <- ExceptT . runMake . make $ modules
-          return (modules, externs, env)
+          (externs, _) <- ExceptT . runMake . make $ modules
+          return (modules, externs)
         case psciBackend of
           Backend setup eval reload (shutdown :: state -> IO ()) ->
             case e of
               Left errs -> do
                 pwd <- getCurrentDirectory
                 putStrLn (P.prettyPrintMultipleErrors P.defaultPPEOptions {P.ppeRelativeDirectory = pwd} errs) >> exitFailure
-              Right (modules, externs, env) -> do
+              Right (modules, externs) -> do
                 historyFilename <- getHistoryFilename
                 let settings = defaultSettings { historyFile = Just historyFilename }
                     initialState = updateLoadedExterns (const (zip (map snd modules) externs)) initialPSCiState
-                    config = PSCiConfig psciInputGlob env
+                    config = PSCiConfig psciInputGlob
                     runner = flip runReaderT config
                              . flip evalStateT initialState
                              . runInputT (setComplete completion settings)
diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -15,7 +15,6 @@
 import qualified Command.Publish as Publish
 import qualified Command.REPL as REPL
 import           Data.Foldable (fold)
-import           Data.Monoid ((<>))
 import qualified Options.Applicative as Opts
 import           System.Environment (getArgs)
 import qualified System.IO as IO
diff --git a/purescript.cabal b/purescript.cabal
--- a/purescript.cabal
+++ b/purescript.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: ed9acbb7111e989600e6d412bddce7d96a240dabdfa42338b1d3a2434ac6c976
+-- hash: 628bcaed9683521da81533454c6e643bda4bea5445007164d4783767f98f0173
 
 name:           purescript
-version:        0.12.0
+version:        0.12.1
 synopsis:       PureScript Programming Language Compiler
 description:    A small strongly, statically typed programming language with expressive types, inspired by Haskell and compiling to JavaScript.
 category:       Language
@@ -108,6 +108,7 @@
     tests/purs/failing/3275-BindingGroupErrorPos.purs
     tests/purs/failing/3275-DataBindingGroupErrorPos.purs
     tests/purs/failing/3335-TypeOpAssociativityError.purs
+    tests/purs/failing/3405.purs
     tests/purs/failing/365.purs
     tests/purs/failing/438.purs
     tests/purs/failing/881.purs
@@ -366,6 +367,8 @@
     tests/purs/passing/3114/VendoredVariant.purs
     tests/purs/passing/3125.purs
     tests/purs/passing/3187-UnusedNameClash.purs
+    tests/purs/passing/3388.purs
+    tests/purs/passing/3410.purs
     tests/purs/passing/652.purs
     tests/purs/passing/810.purs
     tests/purs/passing/862.purs
@@ -659,6 +662,7 @@
     tests/purs/warning/CustomWarning.purs
     tests/purs/warning/CustomWarning2.purs
     tests/purs/warning/CustomWarning3.purs
+    tests/purs/warning/CustomWarning4.purs
     tests/purs/warning/DuplicateExportRef.purs
     tests/purs/warning/DuplicateImport.purs
     tests/purs/warning/DuplicateImportRef.purs
@@ -693,10 +697,10 @@
     tests/purs/warning/UnusedTypeVar.purs
     tests/purs/warning/WildcardInferredType.purs
     tests/support/bower.json
-    tests/support/package-lock.json
     tests/support/package.json
     tests/support/prelude-resolutions.json
-    tests/support/psci/Sample.purs
+    tests/support/psci/Reload.edit
+    tests/support/psci/Reload.purs
     tests/support/pscide/src/CompletionSpecDocs.purs
     tests/support/pscide/src/FindUsage.purs
     tests/support/pscide/src/FindUsage/Definition.purs
@@ -732,11 +736,12 @@
   default-extensions: ConstraintKinds DataKinds DeriveFunctor EmptyDataDecls FlexibleContexts KindSignatures LambdaCase MultiParamTypeClasses NoImplicitPrelude PatternGuards PatternSynonyms RankNTypes RecordWildCards OverloadedStrings ScopedTypeVariables TupleSections ViewPatterns
   ghc-options: -Wall -O2
   build-depends:
-      Glob >=0.9 && <0.10
-    , aeson >=1.0 && <1.3
+      Cabal >=2.2
+    , Glob >=0.9 && <0.10
+    , aeson >=1.0 && <1.4
     , aeson-better-errors >=0.8
     , ansi-terminal >=0.7.1 && <0.9
-    , base >=4.8 && <4.11
+    , base >=4.8 && <4.12
     , base-compat >=0.6.0
     , blaze-html >=0.8.1 && <0.10
     , bower-json >=1.0.0.1 && <1.1
@@ -755,8 +760,8 @@
     , fsnotify >=0.2.1
     , haskeline >=0.7.0.0
     , language-javascript >=0.6.0.9 && <0.7
-    , lens ==4.*
     , lifted-base >=0.2.3 && <0.2.4
+    , microlens-platform >=0.3.9.0 && <0.4
     , monad-control >=1.0.0.0 && <1.1
     , monad-logger >=0.3 && <0.4
     , mtl >=2.1.0 && <2.3.0
@@ -770,7 +775,6 @@
     , scientific >=0.3.4.9 && <0.4
     , semigroups >=0.16.2 && <0.19
     , sourcemap >=0.1.6
-    , spdx ==0.2.*
     , split
     , stm >=0.2.4.0
     , stringsearch
@@ -949,12 +953,13 @@
       app
   ghc-options: -Wall -O2 -fno-warn-unused-do-bind -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      Glob >=0.9 && <0.10
-    , aeson >=1.0 && <1.3
+      Cabal >=2.2
+    , Glob >=0.9 && <0.10
+    , aeson >=1.0 && <1.4
     , aeson-better-errors >=0.8
     , ansi-terminal >=0.7.1 && <0.9
     , ansi-wl-pprint
-    , base >=4.8 && <4.11
+    , base >=4.8 && <4.12
     , base-compat >=0.6.0
     , blaze-html >=0.8.1 && <0.10
     , bower-json >=1.0.0.1 && <1.1
@@ -974,8 +979,8 @@
     , haskeline >=0.7.0.0
     , http-types
     , language-javascript >=0.6.0.9 && <0.7
-    , lens ==4.*
     , lifted-base >=0.2.3 && <0.2.4
+    , microlens-platform >=0.3.9.0 && <0.4
     , monad-control >=1.0.0.0 && <1.1
     , monad-logger >=0.3 && <0.4
     , mtl >=2.1.0 && <2.3.0
@@ -992,7 +997,6 @@
     , scientific >=0.3.4.9 && <0.4
     , semigroups >=0.16.2 && <0.19
     , sourcemap >=0.1.6
-    , spdx ==0.2.*
     , split
     , stm >=0.2.4.0
     , stringsearch
@@ -1035,12 +1039,13 @@
   default-extensions: NoImplicitPrelude
   ghc-options: -Wall
   build-depends:
-      Glob >=0.9 && <0.10
+      Cabal >=2.2
+    , Glob >=0.9 && <0.10
     , HUnit
-    , aeson >=1.0 && <1.3
+    , aeson >=1.0 && <1.4
     , aeson-better-errors >=0.8
     , ansi-terminal >=0.7.1 && <0.9
-    , base >=4.8 && <4.11
+    , base >=4.8 && <4.12
     , base-compat >=0.6.0
     , blaze-html >=0.8.1 && <0.10
     , bower-json >=1.0.0.1 && <1.1
@@ -1061,8 +1066,8 @@
     , hspec
     , hspec-discover
     , language-javascript >=0.6.0.9 && <0.7
-    , lens ==4.*
     , lifted-base >=0.2.3 && <0.2.4
+    , microlens-platform >=0.3.9.0 && <0.4
     , monad-control >=1.0.0.0 && <1.1
     , monad-logger >=0.3 && <0.4
     , mtl >=2.1.0 && <2.3.0
@@ -1077,7 +1082,6 @@
     , scientific >=0.3.4.9 && <0.4
     , semigroups >=0.16.2 && <0.19
     , sourcemap >=0.1.6
-    , spdx ==0.2.*
     , split
     , stm >=0.2.4.0
     , stringsearch
diff --git a/src/Language/PureScript/AST/Binders.hs b/src/Language/PureScript/AST/Binders.hs
--- a/src/Language/PureScript/AST/Binders.hs
+++ b/src/Language/PureScript/AST/Binders.hs
@@ -5,8 +5,6 @@
 
 import Prelude.Compat
 
-import Data.Semigroup
-
 import Language.PureScript.AST.SourcePos
 import Language.PureScript.AST.Literals
 import Language.PureScript.Names
diff --git a/src/Language/PureScript/AST/Declarations.hs b/src/Language/PureScript/AST/Declarations.hs
--- a/src/Language/PureScript/AST/Declarations.hs
+++ b/src/Language/PureScript/AST/Declarations.hs
@@ -124,7 +124,7 @@
   | DuplicateValueDeclaration Ident
   | ArgListLengthsDiffer Ident
   | OverlappingArgNames (Maybe Ident)
-  | MissingClassMember Ident
+  | MissingClassMember (NEL.NonEmpty (Ident, Type))
   | ExtraneousClassMember Ident (Qualified (ProperName 'ClassName))
   | ExpectedType Type Kind
   -- | constructor name, expected argument count, actual argument count
diff --git a/src/Language/PureScript/AST/SourcePos.hs b/src/Language/PureScript/AST/SourcePos.hs
--- a/src/Language/PureScript/AST/SourcePos.hs
+++ b/src/Language/PureScript/AST/SourcePos.hs
@@ -8,7 +8,6 @@
 
 import Control.DeepSeq (NFData)
 import Data.Aeson ((.=), (.:))
-import Data.Monoid
 import Data.Text (Text)
 import GHC.Generics (Generic)
 import Language.PureScript.Comments
diff --git a/src/Language/PureScript/AST/Traversals.hs b/src/Language/PureScript/AST/Traversals.hs
--- a/src/Language/PureScript/AST/Traversals.hs
+++ b/src/Language/PureScript/AST/Traversals.hs
@@ -132,7 +132,7 @@
   f' (BindingGroupDeclaration ds) = BindingGroupDeclaration <$> traverse (\(name, nameKind, val) -> (,,) name nameKind <$> (g val >>= g')) ds
   f' (TypeClassDeclaration sa name args implies deps ds) = TypeClassDeclaration sa name args implies deps <$> traverse (f' <=< f) ds
   f' (TypeInstanceDeclaration sa ch idx name cs className args ds) = TypeInstanceDeclaration sa ch idx name cs className args <$> traverseTypeInstanceBody (traverse (f' <=< f)) ds
-  f' (BoundValueDeclaration sa b expr) = BoundValueDeclaration sa <$> h' b <*> g' expr
+  f' (BoundValueDeclaration sa b expr) = BoundValueDeclaration sa <$> (h' <=< h) b <*> (g' <=< g) expr
   f' other = f other
 
   g' :: Expr -> m Expr
@@ -264,66 +264,66 @@
      , CaseAlternative -> r
      , DoNotationElement -> r
      )
-everythingOnValues (<>) f g h i j = (f', g', h', i', j')
+everythingOnValues (<>.) f g h i j = (f', g', h', i', j')
   where
 
   f' :: Declaration -> r
-  f' d@(DataBindingGroupDeclaration ds) = foldl (<>) (f d) (fmap f' ds)
-  f' d@(ValueDeclaration vd) = foldl (<>) (f d) (fmap h' (valdeclBinders vd) ++ concatMap (\(GuardedExpr grd v) -> fmap k' grd ++ [g' v]) (valdeclExpression vd))
-  f' d@(BindingGroupDeclaration ds) = foldl (<>) (f d) (fmap (\(_, _, val) -> g' val) ds)
-  f' d@(TypeClassDeclaration _ _ _ _ _ ds) = foldl (<>) (f d) (fmap f' ds)
-  f' d@(TypeInstanceDeclaration _ _ _ _ _ _ _ (ExplicitInstance ds)) = foldl (<>) (f d) (fmap f' ds)
-  f' d@(BoundValueDeclaration _ b expr) = f d <> h' b <> g' expr
+  f' d@(DataBindingGroupDeclaration ds) = foldl (<>.) (f d) (fmap f' ds)
+  f' d@(ValueDeclaration vd) = foldl (<>.) (f d) (fmap h' (valdeclBinders vd) ++ concatMap (\(GuardedExpr grd v) -> fmap k' grd ++ [g' v]) (valdeclExpression vd))
+  f' d@(BindingGroupDeclaration ds) = foldl (<>.) (f d) (fmap (\(_, _, val) -> g' val) ds)
+  f' d@(TypeClassDeclaration _ _ _ _ _ ds) = foldl (<>.) (f d) (fmap f' ds)
+  f' d@(TypeInstanceDeclaration _ _ _ _ _ _ _ (ExplicitInstance ds)) = foldl (<>.) (f d) (fmap f' ds)
+  f' d@(BoundValueDeclaration _ b expr) = f d <>. h' b <>. g' expr
   f' d = f d
 
   g' :: Expr -> r
   g' v@(Literal _ l) = lit (g v) g' l
-  g' v@(UnaryMinus _ v1) = g v <> g' v1
-  g' v@(BinaryNoParens op v1 v2) = g v <> g' op <> g' v1 <> g' v2
-  g' v@(Parens v1) = g v <> g' v1
-  g' v@(TypeClassDictionaryConstructorApp _ v1) = g v <> g' v1
-  g' v@(Accessor _ v1) = g v <> g' v1
-  g' v@(ObjectUpdate obj vs) = foldl (<>) (g v <> g' obj) (fmap (g' . snd) vs)
-  g' v@(ObjectUpdateNested obj vs) = foldl (<>) (g v <> g' obj) (fmap g' vs)
-  g' v@(Abs b v1) = g v <> h' b <> g' v1
-  g' v@(App v1 v2) = g v <> g' v1 <> g' v2
-  g' v@(IfThenElse v1 v2 v3) = g v <> g' v1 <> g' v2 <> g' v3
-  g' v@(Case vs alts) = foldl (<>) (foldl (<>) (g v) (fmap g' vs)) (fmap i' alts)
-  g' v@(TypedValue _ v1 _) = g v <> g' v1
-  g' v@(Let _ ds v1) = foldl (<>) (g v) (fmap f' ds) <> g' v1
-  g' v@(Do es) = foldl (<>) (g v) (fmap j' es)
-  g' v@(Ado es v1) = foldl (<>) (g v) (fmap j' es) <> g' v1
-  g' v@(PositionedValue _ _ v1) = g v <> g' v1
+  g' v@(UnaryMinus _ v1) = g v <>. g' v1
+  g' v@(BinaryNoParens op v1 v2) = g v <>. g' op <>. g' v1 <>. g' v2
+  g' v@(Parens v1) = g v <>. g' v1
+  g' v@(TypeClassDictionaryConstructorApp _ v1) = g v <>. g' v1
+  g' v@(Accessor _ v1) = g v <>. g' v1
+  g' v@(ObjectUpdate obj vs) = foldl (<>.) (g v <>. g' obj) (fmap (g' . snd) vs)
+  g' v@(ObjectUpdateNested obj vs) = foldl (<>.) (g v <>. g' obj) (fmap g' vs)
+  g' v@(Abs b v1) = g v <>. h' b <>. g' v1
+  g' v@(App v1 v2) = g v <>. g' v1 <>. g' v2
+  g' v@(IfThenElse v1 v2 v3) = g v <>. g' v1 <>. g' v2 <>. g' v3
+  g' v@(Case vs alts) = foldl (<>.) (foldl (<>.) (g v) (fmap g' vs)) (fmap i' alts)
+  g' v@(TypedValue _ v1 _) = g v <>. g' v1
+  g' v@(Let _ ds v1) = foldl (<>.) (g v) (fmap f' ds) <>. g' v1
+  g' v@(Do es) = foldl (<>.) (g v) (fmap j' es)
+  g' v@(Ado es v1) = foldl (<>.) (g v) (fmap j' es) <>. g' v1
+  g' v@(PositionedValue _ _ v1) = g v <>. g' v1
   g' v = g v
 
   h' :: Binder -> r
   h' b@(LiteralBinder _ l) = lit (h b) h' l
-  h' b@(ConstructorBinder _ _ bs) = foldl (<>) (h b) (fmap h' bs)
-  h' b@(BinaryNoParensBinder b1 b2 b3) = h b <> h' b1 <> h' b2 <> h' b3
-  h' b@(ParensInBinder b1) = h b <> h' b1
-  h' b@(NamedBinder _ _ b1) = h b <> h' b1
-  h' b@(PositionedBinder _ _ b1) = h b <> h' b1
-  h' b@(TypedBinder _ b1) = h b <> h' b1
+  h' b@(ConstructorBinder _ _ bs) = foldl (<>.) (h b) (fmap h' bs)
+  h' b@(BinaryNoParensBinder b1 b2 b3) = h b <>. h' b1 <>. h' b2 <>. h' b3
+  h' b@(ParensInBinder b1) = h b <>. h' b1
+  h' b@(NamedBinder _ _ b1) = h b <>. h' b1
+  h' b@(PositionedBinder _ _ b1) = h b <>. h' b1
+  h' b@(TypedBinder _ b1) = h b <>. h' b1
   h' b = h b
 
   lit :: r -> (a -> r) -> Literal a -> r
-  lit r go (ArrayLiteral as) = foldl (<>) r (fmap go as)
-  lit r go (ObjectLiteral as) = foldl (<>) r (fmap (go . snd) as)
+  lit r go (ArrayLiteral as) = foldl (<>.) r (fmap go as)
+  lit r go (ObjectLiteral as) = foldl (<>.) r (fmap (go . snd) as)
   lit r _ _ = r
 
   i' :: CaseAlternative -> r
   i' ca@(CaseAlternative bs gs) =
-    foldl (<>) (i ca) (fmap h' bs ++ concatMap (\(GuardedExpr grd val) -> fmap k' grd ++ [g' val]) gs)
+    foldl (<>.) (i ca) (fmap h' bs ++ concatMap (\(GuardedExpr grd val) -> fmap k' grd ++ [g' val]) gs)
 
   j' :: DoNotationElement -> r
-  j' e@(DoNotationValue v) = j e <> g' v
-  j' e@(DoNotationBind b v) = j e <> h' b <> g' v
-  j' e@(DoNotationLet ds) = foldl (<>) (j e) (fmap f' ds)
-  j' e@(PositionedDoNotationElement _ _ e1) = j e <> j' e1
+  j' e@(DoNotationValue v) = j e <>. g' v
+  j' e@(DoNotationBind b v) = j e <>. h' b <>. g' v
+  j' e@(DoNotationLet ds) = foldl (<>.) (j e) (fmap f' ds)
+  j' e@(PositionedDoNotationElement _ _ e1) = j e <>. j' e1
 
   k' :: Guard -> r
   k' (ConditionGuard e) = g' e
-  k' (PatternGuard b e) = h' b <> g' e
+  k' (PatternGuard b e) = h' b <>. g' e
 
 everythingWithContextOnValues
   :: forall s r
@@ -340,50 +340,50 @@
      , Binder            -> r
      , CaseAlternative   -> r
      , DoNotationElement -> r)
-everythingWithContextOnValues s0 r0 (<>) f g h i j = (f'' s0, g'' s0, h'' s0, i'' s0, j'' s0)
+everythingWithContextOnValues s0 r0 (<>.) f g h i j = (f'' s0, g'' s0, h'' s0, i'' s0, j'' s0)
   where
 
   f'' :: s -> Declaration -> r
-  f'' s d = let (s', r) = f s d in r <> f' s' d
+  f'' s d = let (s', r) = f s d in r <>. f' s' d
 
   f' :: s -> Declaration -> r
-  f' s (DataBindingGroupDeclaration ds) = foldl (<>) r0 (fmap (f'' s) ds)
-  f' s (ValueDeclaration vd) = foldl (<>) r0 (fmap (h'' s) (valdeclBinders vd) ++ concatMap (\(GuardedExpr grd v) -> fmap (k' s) grd ++ [g'' s v]) (valdeclExpression vd))
-  f' s (BindingGroupDeclaration ds) = foldl (<>) r0 (fmap (\(_, _, val) -> g'' s val) ds)
-  f' s (TypeClassDeclaration _ _ _ _ _ ds) = foldl (<>) r0 (fmap (f'' s) ds)
-  f' s (TypeInstanceDeclaration _ _ _ _ _ _ _ (ExplicitInstance ds)) = foldl (<>) r0 (fmap (f'' s) ds)
+  f' s (DataBindingGroupDeclaration ds) = foldl (<>.) r0 (fmap (f'' s) ds)
+  f' s (ValueDeclaration vd) = foldl (<>.) r0 (fmap (h'' s) (valdeclBinders vd) ++ concatMap (\(GuardedExpr grd v) -> fmap (k' s) grd ++ [g'' s v]) (valdeclExpression vd))
+  f' s (BindingGroupDeclaration ds) = foldl (<>.) r0 (fmap (\(_, _, val) -> g'' s val) ds)
+  f' s (TypeClassDeclaration _ _ _ _ _ ds) = foldl (<>.) r0 (fmap (f'' s) ds)
+  f' s (TypeInstanceDeclaration _ _ _ _ _ _ _ (ExplicitInstance ds)) = foldl (<>.) r0 (fmap (f'' s) ds)
   f' _ _ = r0
 
   g'' :: s -> Expr -> r
-  g'' s v = let (s', r) = g s v in r <> g' s' v
+  g'' s v = let (s', r) = g s v in r <>. g' s' v
 
   g' :: s -> Expr -> r
   g' s (Literal _ l) = lit g'' s l
   g' s (UnaryMinus _ v1) = g'' s v1
-  g' s (BinaryNoParens op v1 v2) = g'' s op <> g'' s v1 <> g'' s v2
+  g' s (BinaryNoParens op v1 v2) = g'' s op <>. g'' s v1 <>. g'' s v2
   g' s (Parens v1) = g'' s v1
   g' s (TypeClassDictionaryConstructorApp _ v1) = g'' s v1
   g' s (Accessor _ v1) = g'' s v1
-  g' s (ObjectUpdate obj vs) = foldl (<>) (g'' s obj) (fmap (g'' s . snd) vs)
-  g' s (ObjectUpdateNested obj vs) = foldl (<>) (g'' s obj) (fmap (g'' s) vs)
-  g' s (Abs binder v1) = h'' s binder <> g'' s v1
-  g' s (App v1 v2) = g'' s v1 <> g'' s v2
-  g' s (IfThenElse v1 v2 v3) = g'' s v1 <> g'' s v2 <> g'' s v3
-  g' s (Case vs alts) = foldl (<>) (foldl (<>) r0 (fmap (g'' s) vs)) (fmap (i'' s) alts)
+  g' s (ObjectUpdate obj vs) = foldl (<>.) (g'' s obj) (fmap (g'' s . snd) vs)
+  g' s (ObjectUpdateNested obj vs) = foldl (<>.) (g'' s obj) (fmap (g'' s) vs)
+  g' s (Abs binder v1) = h'' s binder <>. g'' s v1
+  g' s (App v1 v2) = g'' s v1 <>. g'' s v2
+  g' s (IfThenElse v1 v2 v3) = g'' s v1 <>. g'' s v2 <>. g'' s v3
+  g' s (Case vs alts) = foldl (<>.) (foldl (<>.) r0 (fmap (g'' s) vs)) (fmap (i'' s) alts)
   g' s (TypedValue _ v1 _) = g'' s v1
-  g' s (Let _ ds v1) = foldl (<>) r0 (fmap (f'' s) ds) <> g'' s v1
-  g' s (Do es) = foldl (<>) r0 (fmap (j'' s) es)
-  g' s (Ado es v1) = foldl (<>) r0 (fmap (j'' s) es) <> g'' s v1
+  g' s (Let _ ds v1) = foldl (<>.) r0 (fmap (f'' s) ds) <>. g'' s v1
+  g' s (Do es) = foldl (<>.) r0 (fmap (j'' s) es)
+  g' s (Ado es v1) = foldl (<>.) r0 (fmap (j'' s) es) <>. g'' s v1
   g' s (PositionedValue _ _ v1) = g'' s v1
   g' _ _ = r0
 
   h'' :: s -> Binder -> r
-  h'' s b = let (s', r) = h s b in r <> h' s' b
+  h'' s b = let (s', r) = h s b in r <>. h' s' b
 
   h' :: s -> Binder -> r
   h' s (LiteralBinder _ l) = lit h'' s l
-  h' s (ConstructorBinder _ _ bs) = foldl (<>) r0 (fmap (h'' s) bs)
-  h' s (BinaryNoParensBinder b1 b2 b3) = h'' s b1 <> h'' s b2 <> h'' s b3
+  h' s (ConstructorBinder _ _ bs) = foldl (<>.) r0 (fmap (h'' s) bs)
+  h' s (BinaryNoParensBinder b1 b2 b3) = h'' s b1 <>. h'' s b2 <>. h'' s b3
   h' s (ParensInBinder b) = h'' s b
   h' s (NamedBinder _ _ b1) = h'' s b1
   h' s (PositionedBinder _ _ b1) = h'' s b1
@@ -391,28 +391,28 @@
   h' _ _ = r0
 
   lit :: (s -> a -> r) -> s -> Literal a -> r
-  lit go s (ArrayLiteral as) = foldl (<>) r0 (fmap (go s) as)
-  lit go s (ObjectLiteral as) = foldl (<>) r0 (fmap (go s . snd) as)
+  lit go s (ArrayLiteral as) = foldl (<>.) r0 (fmap (go s) as)
+  lit go s (ObjectLiteral as) = foldl (<>.) r0 (fmap (go s . snd) as)
   lit _ _ _ = r0
 
   i'' :: s -> CaseAlternative -> r
-  i'' s ca = let (s', r) = i s ca in r <> i' s' ca
+  i'' s ca = let (s', r) = i s ca in r <>. i' s' ca
 
   i' :: s -> CaseAlternative -> r
-  i' s (CaseAlternative bs gs) = foldl (<>) r0 (fmap (h'' s) bs ++ concatMap (\(GuardedExpr grd val) -> fmap (k' s) grd ++ [g'' s val]) gs)
+  i' s (CaseAlternative bs gs) = foldl (<>.) r0 (fmap (h'' s) bs ++ concatMap (\(GuardedExpr grd val) -> fmap (k' s) grd ++ [g'' s val]) gs)
 
   j'' :: s -> DoNotationElement -> r
-  j'' s e = let (s', r) = j s e in r <> j' s' e
+  j'' s e = let (s', r) = j s e in r <>. j' s' e
 
   j' :: s -> DoNotationElement -> r
   j' s (DoNotationValue v) = g'' s v
-  j' s (DoNotationBind b v) = h'' s b <> g'' s v
-  j' s (DoNotationLet ds) = foldl (<>) r0 (fmap (f'' s) ds)
+  j' s (DoNotationBind b v) = h'' s b <>. g'' s v
+  j' s (DoNotationLet ds) = foldl (<>.) r0 (fmap (f'' s) ds)
   j' s (PositionedDoNotationElement _ _ e1) = j'' s e1
 
   k' :: s -> Guard -> r
   k' s (ConditionGuard e) = g'' s e
-  k' s (PatternGuard b e) = h'' s b <> g'' s e
+  k' s (PatternGuard b e) = h'' s b <>. g'' s e
 
 everywhereWithContextOnValuesM
   :: forall m s
@@ -514,9 +514,6 @@
      )
 everythingWithScope f g h i j = (f'', g'', h'', i'', \s -> snd . j'' s)
   where
-  -- Avoid importing Data.Monoid and getting shadowed names above
-  (<>) = mappend
-
   f'' :: S.Set ScopedIdent -> Declaration -> r
   f'' s a = f s a <> f' s a
 
@@ -635,7 +632,7 @@
   forDecls (DataDeclaration _ _ _ _ dctors) = mconcat (concatMap (fmap f . snd) dctors)
   forDecls (ExternDeclaration _ _ ty) = f ty
   forDecls (TypeClassDeclaration _ _ _ implies _ _) = mconcat (concatMap (fmap f . constraintArgs) implies)
-  forDecls (TypeInstanceDeclaration _ _ _ _ cs _ tys _) = mconcat (concatMap (fmap f . constraintArgs) cs) `mappend` mconcat (fmap f tys)
+  forDecls (TypeInstanceDeclaration _ _ _ _ cs _ tys _) = mconcat (concatMap (fmap f . constraintArgs) cs) <> mconcat (fmap f tys)
   forDecls (TypeSynonymDeclaration _ _ _ ty) = f ty
   forDecls (TypeDeclaration td) = f (tydeclType td)
   forDecls _ = mempty
@@ -657,16 +654,16 @@
 accumKinds f = everythingOnValues mappend forDecls forValues (const mempty) (const mempty) (const mempty)
   where
   forDecls (DataDeclaration _ _ _ args dctors) =
-    foldMap (foldMap f . snd) args `mappend`
+    foldMap (foldMap f . snd) args <>
     foldMap (foldMap forTypes . snd) dctors
   forDecls (TypeClassDeclaration _ _ args implies _ _) =
-    foldMap (foldMap f . snd) args `mappend`
+    foldMap (foldMap f . snd) args <>
     foldMap (foldMap forTypes . constraintArgs) implies
   forDecls (TypeInstanceDeclaration _ _ _ _ cs _ tys _) =
-    foldMap (foldMap forTypes . constraintArgs) cs `mappend`
+    foldMap (foldMap forTypes . constraintArgs) cs <>
     foldMap forTypes tys
   forDecls (TypeSynonymDeclaration _ _ args ty) =
-    foldMap (foldMap f . snd) args `mappend`
+    foldMap (foldMap f . snd) args <>
     forTypes ty
   forDecls (TypeDeclaration td) = forTypes (tydeclType td)
   forDecls (ExternDeclaration _ _ ty) = forTypes ty
diff --git a/src/Language/PureScript/CodeGen/JS.hs b/src/Language/PureScript/CodeGen/JS.hs
--- a/src/Language/PureScript/CodeGen/JS.hs
+++ b/src/Language/PureScript/CodeGen/JS.hs
@@ -19,7 +19,6 @@
 import qualified Data.Foldable as F
 import qualified Data.Map as M
 import Data.Maybe (fromMaybe, isNothing)
-import Data.Monoid ((<>))
 import Data.String (fromString)
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/src/Language/PureScript/CodeGen/JS/Common.hs b/src/Language/PureScript/CodeGen/JS/Common.hs
--- a/src/Language/PureScript/CodeGen/JS/Common.hs
+++ b/src/Language/PureScript/CodeGen/JS/Common.hs
@@ -4,7 +4,6 @@
 import Prelude.Compat
 
 import Data.Char
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 
diff --git a/src/Language/PureScript/CodeGen/JS/Printer.hs b/src/Language/PureScript/CodeGen/JS/Printer.hs
--- a/src/Language/PureScript/CodeGen/JS/Printer.hs
+++ b/src/Language/PureScript/CodeGen/JS/Printer.hs
@@ -13,7 +13,6 @@
 import qualified Control.Arrow as A
 
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 
diff --git a/src/Language/PureScript/Constants.hs b/src/Language/PureScript/Constants.hs
--- a/src/Language/PureScript/Constants.hs
+++ b/src/Language/PureScript/Constants.hs
@@ -204,29 +204,23 @@
 
 -- Core lib values
 
-untilE :: forall a. (IsString a) => a
-untilE = "untilE"
-
-whileE :: forall a. (IsString a) => a
-whileE = "whileE"
-
 runST :: forall a. (IsString a) => a
-runST = "runST"
+runST = "run"
 
 stRefValue :: forall a. (IsString a) => a
 stRefValue = "value"
 
 newSTRef :: forall a. (IsString a) => a
-newSTRef = "newSTRef"
+newSTRef = "new"
 
 readSTRef :: forall a. (IsString a) => a
-readSTRef = "readSTRef"
+readSTRef = "read"
 
 writeSTRef :: forall a. (IsString a) => a
-writeSTRef = "writeSTRef"
+writeSTRef = "write"
 
 modifySTRef :: forall a. (IsString a) => a
-modifySTRef = "modifySTRef"
+modifySTRef = "modify"
 
 mkFn :: forall a. (IsString a) => a
 mkFn = "mkFn"
@@ -257,6 +251,8 @@
   { edApplicativeDict :: PSString
   , edBindDict :: PSString
   , edMonadDict :: PSString
+  , edWhile :: PSString
+  , edUntil :: PSString
   }
 
 effDictionaries :: EffectDictionaries
@@ -264,6 +260,8 @@
   { edApplicativeDict = "applicativeEff"
   , edBindDict = "bindEff"
   , edMonadDict = "monadEff"
+  , edWhile = "whileE"
+  , edUntil = "untilE"
   }
 
 effectDictionaries :: EffectDictionaries
@@ -271,8 +269,19 @@
   { edApplicativeDict = "applicativeEffect"
   , edBindDict = "bindEffect"
   , edMonadDict = "monadEffect"
+  , edWhile = "whileE"
+  , edUntil = "untilE"
   }
 
+stDictionaries :: EffectDictionaries
+stDictionaries = EffectDictionaries
+  { edApplicativeDict = "applicativeST"
+  , edBindDict = "bindST"
+  , edMonadDict = "monadST"
+  , edWhile = "while"
+  , edUntil = "until"
+  }
+
 discardUnitDictionary :: forall a. (IsString a) => a
 discardUnitDictionary = "discardUnit"
 
@@ -507,7 +516,7 @@
 effect = "Effect"
 
 st :: forall a. (IsString a) => a
-st = "Control_Monad_ST"
+st = "Control_Monad_ST_Internal"
 
 controlApplicative :: forall a. (IsString a) => a
 controlApplicative = "Control_Applicative"
diff --git a/src/Language/PureScript/CoreFn/Traversals.hs b/src/Language/PureScript/CoreFn/Traversals.hs
--- a/src/Language/PureScript/CoreFn/Traversals.hs
+++ b/src/Language/PureScript/CoreFn/Traversals.hs
@@ -50,27 +50,27 @@
                       (Binder a -> r) ->
                       (CaseAlternative a -> r) ->
                       (Bind a -> r, Expr a -> r, Binder a -> r, CaseAlternative a -> r)
-everythingOnValues (<>) f g h i = (f', g', h', i')
+everythingOnValues (<>.) f g h i = (f', g', h', i')
   where
-  f' b@(NonRec _ _ e) = f b <> g' e
-  f' b@(Rec es) = foldl (<>) (f b) (map (g' . snd) es)
+  f' b@(NonRec _ _ e) = f b <>. g' e
+  f' b@(Rec es) = foldl (<>.) (f b) (map (g' . snd) es)
 
-  g' v@(Literal _ l) = foldl (<>) (g v) (map g' (extractLiteral l))
-  g' v@(Accessor _ _ e1) = g v <> g' e1
-  g' v@(ObjectUpdate _ obj vs) = foldl (<>) (g v <> g' obj) (map (g' . snd) vs)
-  g' v@(Abs _ _ e1) = g v <> g' e1
-  g' v@(App _ e1 e2) = g v <> g' e1 <> g' e2
-  g' v@(Case _ vs alts) = foldl (<>) (foldl (<>) (g v) (map g' vs)) (map i' alts)
-  g' v@(Let _ ds e1) = foldl (<>) (g v) (map f' ds) <> g' e1
+  g' v@(Literal _ l) = foldl (<>.) (g v) (map g' (extractLiteral l))
+  g' v@(Accessor _ _ e1) = g v <>. g' e1
+  g' v@(ObjectUpdate _ obj vs) = foldl (<>.) (g v <>. g' obj) (map (g' . snd) vs)
+  g' v@(Abs _ _ e1) = g v <>. g' e1
+  g' v@(App _ e1 e2) = g v <>. g' e1 <>. g' e2
+  g' v@(Case _ vs alts) = foldl (<>.) (foldl (<>.) (g v) (map g' vs)) (map i' alts)
+  g' v@(Let _ ds e1) = foldl (<>.) (g v) (map f' ds) <>. g' e1
   g' v = g v
 
-  h' b@(LiteralBinder _ l) = foldl (<>) (h b) (map h' (extractLiteral l))
-  h' b@(ConstructorBinder _ _ _ bs) = foldl (<>) (h b) (map h' bs)
-  h' b@(NamedBinder _ _ b1) = h b <> h' b1
+  h' b@(LiteralBinder _ l) = foldl (<>.) (h b) (map h' (extractLiteral l))
+  h' b@(ConstructorBinder _ _ _ bs) = foldl (<>.) (h b) (map h' bs)
+  h' b@(NamedBinder _ _ b1) = h b <>. h' b1
   h' b = h b
 
-  i' ca@(CaseAlternative bs (Right val)) = foldl (<>) (i ca) (map h' bs) <> g' val
-  i' ca@(CaseAlternative bs (Left gs)) = foldl (<>) (i ca) (map h' bs ++ concatMap (\(grd, val) -> [g' grd, g' val]) gs)
+  i' ca@(CaseAlternative bs (Right val)) = foldl (<>.) (i ca) (map h' bs) <>. g' val
+  i' ca@(CaseAlternative bs (Left gs)) = foldl (<>.) (i ca) (map h' bs ++ concatMap (\(grd, val) -> [g' grd, g' val]) gs)
 
   extractLiteral (ArrayLiteral xs) = xs
   extractLiteral (ObjectLiteral xs) = map snd xs
diff --git a/src/Language/PureScript/CoreImp/AST.hs b/src/Language/PureScript/CoreImp/AST.hs
--- a/src/Language/PureScript/CoreImp/AST.hs
+++ b/src/Language/PureScript/CoreImp/AST.hs
@@ -201,24 +201,24 @@
   go other = f other
 
 everything :: (r -> r -> r) -> (AST -> r) -> AST -> r
-everything (<>) f = go where
-  go j@(Unary _ _ j1) = f j <> go j1
-  go j@(Binary _ _ j1 j2) = f j <> go j1 <> go j2
-  go j@(ArrayLiteral _ js) = foldl (<>) (f j) (map go js)
-  go j@(Indexer _ j1 j2) = f j <> go j1 <> go j2
-  go j@(ObjectLiteral _ js) = foldl (<>) (f j) (map (go . snd) js)
-  go j@(Function _ _ _ j1) = f j <> go j1
-  go j@(App _ j1 js) = foldl (<>) (f j <> go j1) (map go js)
-  go j@(Block _ js) = foldl (<>) (f j) (map go js)
-  go j@(VariableIntroduction _ _ (Just j1)) = f j <> go j1
-  go j@(Assignment _ j1 j2) = f j <> go j1 <> go j2
-  go j@(While _ j1 j2) = f j <> go j1 <> go j2
-  go j@(For _ _ j1 j2 j3) = f j <> go j1 <> go j2 <> go j3
-  go j@(ForIn _ _ j1 j2) = f j <> go j1 <> go j2
-  go j@(IfElse _ j1 j2 Nothing) = f j <> go j1 <> go j2
-  go j@(IfElse _ j1 j2 (Just j3)) = f j <> go j1 <> go j2 <> go j3
-  go j@(Return _ j1) = f j <> go j1
-  go j@(Throw _ j1) = f j <> go j1
-  go j@(InstanceOf _ j1 j2) = f j <> go j1 <> go j2
-  go j@(Comment _ _ j1) = f j <> go j1
+everything (<>.) f = go where
+  go j@(Unary _ _ j1) = f j <>. go j1
+  go j@(Binary _ _ j1 j2) = f j <>. go j1 <>. go j2
+  go j@(ArrayLiteral _ js) = foldl (<>.) (f j) (map go js)
+  go j@(Indexer _ j1 j2) = f j <>. go j1 <>. go j2
+  go j@(ObjectLiteral _ js) = foldl (<>.) (f j) (map (go . snd) js)
+  go j@(Function _ _ _ j1) = f j <>. go j1
+  go j@(App _ j1 js) = foldl (<>.) (f j <>. go j1) (map go js)
+  go j@(Block _ js) = foldl (<>.) (f j) (map go js)
+  go j@(VariableIntroduction _ _ (Just j1)) = f j <>. go j1
+  go j@(Assignment _ j1 j2) = f j <>. go j1 <>. go j2
+  go j@(While _ j1 j2) = f j <>. go j1 <>. go j2
+  go j@(For _ _ j1 j2 j3) = f j <>. go j1 <>. go j2 <>. go j3
+  go j@(ForIn _ _ j1 j2) = f j <>. go j1 <>. go j2
+  go j@(IfElse _ j1 j2 Nothing) = f j <>. go j1 <>. go j2
+  go j@(IfElse _ j1 j2 (Just j3)) = f j <>. go j1 <>. go j2 <>. go j3
+  go j@(Return _ j1) = f j <>. go j1
+  go j@(Throw _ j1) = f j <>. go j1
+  go j@(InstanceOf _ j1 j2) = f j <>. go j1 <>. go j2
+  go j@(Comment _ _ j1) = f j <>. go j1
   go other = f other
diff --git a/src/Language/PureScript/CoreImp/Optimizer.hs b/src/Language/PureScript/CoreImp/Optimizer.hs
--- a/src/Language/PureScript/CoreImp/Optimizer.hs
+++ b/src/Language/PureScript/CoreImp/Optimizer.hs
@@ -38,8 +38,9 @@
       , inlineCommonOperators
       ]) js
     untilFixedPoint (return . tidyUp) . tco . inlineST
-      =<< untilFixedPoint (return . magicDo')
-      =<< untilFixedPoint (return . magicDo) js'
+      =<< untilFixedPoint (return . magicDoST)
+      =<< untilFixedPoint (return . magicDoEff)
+      =<< untilFixedPoint (return . magicDoEffect) js'
   where
     tidyUp :: AST -> AST
     tidyUp = applyAll
diff --git a/src/Language/PureScript/CoreImp/Optimizer/Inliner.hs b/src/Language/PureScript/CoreImp/Optimizer/Inliner.hs
--- a/src/Language/PureScript/CoreImp/Optimizer/Inliner.hs
+++ b/src/Language/PureScript/CoreImp/Optimizer/Inliner.hs
@@ -16,7 +16,6 @@
 import Control.Monad.Supply.Class (MonadSupply, freshName)
 
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import Data.String (IsString, fromString)
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/src/Language/PureScript/CoreImp/Optimizer/MagicDo.hs b/src/Language/PureScript/CoreImp/Optimizer/MagicDo.hs
--- a/src/Language/PureScript/CoreImp/Optimizer/MagicDo.hs
+++ b/src/Language/PureScript/CoreImp/Optimizer/MagicDo.hs
@@ -1,6 +1,6 @@
 -- | This module implements the "Magic Do" optimization, which inlines calls to return
 -- and bind for the Eff monad, as well as some of its actions.
-module Language.PureScript.CoreImp.Optimizer.MagicDo (magicDo, magicDo', inlineST) where
+module Language.PureScript.CoreImp.Optimizer.MagicDo (magicDoEffect, magicDoEff, magicDoST, inlineST) where
 
 import Prelude.Compat
 import Protolude (ordNub)
@@ -27,14 +27,17 @@
 --    var x = m1();
 --    ...
 --  }
-magicDo :: AST -> AST
-magicDo = magicDo'' C.eff C.effDictionaries
+magicDoEff :: AST -> AST
+magicDoEff = magicDo C.eff C.effDictionaries
 
-magicDo' :: AST -> AST
-magicDo' = magicDo'' C.effect C.effectDictionaries
+magicDoEffect :: AST -> AST
+magicDoEffect = magicDo C.effect C.effectDictionaries
 
-magicDo'' :: Text -> C.EffectDictionaries -> AST -> AST
-magicDo'' effectModule C.EffectDictionaries{..} = everywhereTopDown convert
+magicDoST :: AST -> AST
+magicDoST = magicDo C.st C.stDictionaries
+
+magicDo :: Text -> C.EffectDictionaries -> AST -> AST
+magicDo effectModule C.EffectDictionaries{..} = everywhereTopDown convert
   where
   -- The name of the function block which is added to denote a do block
   fnName = "__do"
@@ -49,10 +52,10 @@
   convert (App _ (App _ bind [m]) [Function s1 Nothing [arg] (Block s2 js)]) | isBind bind =
     Function s1 (Just fnName) [] $ Block s2 (VariableIntroduction s2 arg (Just (App s2 m [])) : map applyReturns js)
   -- Desugar untilE
-  convert (App s1 (App _ f [arg]) []) | isEffFunc C.untilE f =
+  convert (App s1 (App _ f [arg]) []) | isEffFunc edUntil f =
     App s1 (Function s1 Nothing [] (Block s1 [ While s1 (Unary s1 Not (App s1 arg [])) (Block s1 []), Return s1 $ ObjectLiteral s1 []])) []
   -- Desugar whileE
-  convert (App _ (App _ (App s1 f [arg1]) [arg2]) []) | isEffFunc C.whileE f =
+  convert (App _ (App _ (App s1 f [arg1]) [arg2]) []) | isEffFunc edWhile f =
     App s1 (Function s1 Nothing [] (Block s1 [ While s1 (App s1 arg1 []) (Block s1 [ App s1 arg2 [] ]), Return s1 $ ObjectLiteral s1 []])) []
   -- Inline __do returns
   convert (Return _ (App _ (Function _ (Just ident) [] body) [])) | ident == fnName = body
@@ -98,12 +101,12 @@
   -- Look for runST blocks and inline the STRefs there.
   -- If all STRefs are used in the scope of the same runST, only using { read, write, modify }STRef then
   -- we can be more aggressive about inlining, and actually turn STRefs into local variables.
-  convertBlock (App _ f [arg]) | isSTFunc C.runST f =
+  convertBlock (App s1 f [arg]) | isSTFunc C.runST f =
     let refs = ordNub . findSTRefsIn $ arg
         usages = findAllSTUsagesIn arg
         allUsagesAreLocalVars = all (\u -> let v = toVar u in isJust v && fromJust v `elem` refs) usages
         localVarsDoNotEscape = all (\r -> length (r `appearingIn` arg) == length (filter (\u -> let v = toVar u in v == Just r) usages)) refs
-    in everywhere (convert (allUsagesAreLocalVars && localVarsDoNotEscape)) arg
+    in App s1 (everywhere (convert (allUsagesAreLocalVars && localVarsDoNotEscape)) arg) []
   convertBlock other = other
   -- Convert a block in a safe way, preserving object wrappers of references,
   -- or in a more aggressive way, turning wrappers into local variables depending on the
@@ -112,9 +115,9 @@
    Function s1 Nothing [] (Block s1 [Return s1 $ if agg then arg else ObjectLiteral s1 [(mkString C.stRefValue, arg)]])
   convert agg (App _ (App s1 f [ref]) []) | isSTFunc C.readSTRef f =
     if agg then ref else Indexer s1 (StringLiteral s1 C.stRefValue) ref
-  convert agg (App _ (App _ (App s1 f [ref]) [arg]) []) | isSTFunc C.writeSTRef f =
+  convert agg (App _ (App _ (App s1 f [arg]) [ref]) []) | isSTFunc C.writeSTRef f =
     if agg then Assignment s1 ref arg else Assignment s1 (Indexer s1 (StringLiteral s1 C.stRefValue) ref) arg
-  convert agg (App _ (App _ (App s1 f [ref]) [func]) []) | isSTFunc C.modifySTRef f =
+  convert agg (App _ (App _ (App s1 f [func]) [ref]) []) | isSTFunc C.modifySTRef f =
     if agg then Assignment s1 ref (App s1 func [ref]) else Assignment s1 (Indexer s1 (StringLiteral s1 C.stRefValue) ref) (App s1 func [Indexer s1 (StringLiteral s1 C.stRefValue) ref])
   convert _ other = other
   -- Check if an expression represents a function in the ST module
@@ -129,7 +132,7 @@
   findAllSTUsagesIn = everything (++) isSTUsage
     where
     isSTUsage (App _ (App _ f [ref]) []) | isSTFunc C.readSTRef f = [ref]
-    isSTUsage (App _ (App _ (App _ f [ref]) [_]) []) | isSTFunc C.writeSTRef f || isSTFunc C.modifySTRef f = [ref]
+    isSTUsage (App _ (App _ (App _ f [_]) [ref]) []) | isSTFunc C.writeSTRef f || isSTFunc C.modifySTRef f = [ref]
     isSTUsage _ = []
   -- Find all uses of a variable
   appearingIn ref = everything (++) isVar
diff --git a/src/Language/PureScript/CoreImp/Optimizer/TCO.hs b/src/Language/PureScript/CoreImp/Optimizer/TCO.hs
--- a/src/Language/PureScript/CoreImp/Optimizer/TCO.hs
+++ b/src/Language/PureScript/CoreImp/Optimizer/TCO.hs
@@ -4,7 +4,6 @@
 import Prelude.Compat
 
 import Data.Text (Text)
-import Data.Monoid ((<>))
 import Language.PureScript.CoreImp.AST
 import Language.PureScript.AST.SourcePos (SourceSpan)
 import Safe (headDef, tailSafe)
diff --git a/src/Language/PureScript/Docs/AsHtml.hs b/src/Language/PureScript/Docs/AsHtml.hs
--- a/src/Language/PureScript/Docs/AsHtml.hs
+++ b/src/Language/PureScript/Docs/AsHtml.hs
@@ -20,7 +20,6 @@
 import Data.Char (isUpper)
 import Data.Either (isRight)
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import Data.Foldable (for_)
 import Data.String (fromString)
 
diff --git a/src/Language/PureScript/Docs/AsMarkdown.hs b/src/Language/PureScript/Docs/AsMarkdown.hs
--- a/src/Language/PureScript/Docs/AsMarkdown.hs
+++ b/src/Language/PureScript/Docs/AsMarkdown.hs
@@ -13,7 +13,6 @@
 import Control.Monad.Writer (Writer, tell, execWriter)
 
 import Data.Foldable (for_)
-import Data.Monoid ((<>))
 import Data.List (partition)
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/src/Language/PureScript/Docs/Convert/ReExports.hs b/src/Language/PureScript/Docs/Convert/ReExports.hs
--- a/src/Language/PureScript/Docs/Convert/ReExports.hs
+++ b/src/Language/PureScript/Docs/Convert/ReExports.hs
@@ -14,7 +14,6 @@
 import Data.Either
 import Data.Map (Map)
 import Data.Maybe (mapMaybe)
-import Data.Monoid ((<>))
 import qualified Data.Map as Map
 import Data.Text (Text)
 import qualified Data.Text as T
@@ -415,12 +414,13 @@
   }
   deriving (Show)
 
+instance Semigroup TypeClassEnv where
+  (TypeClassEnv a1 b1 c1) <> (TypeClassEnv a2 b2 c2) =
+    TypeClassEnv (a1 <> a2) (b1 <> b2) (c1 <> c2)
+
 instance Monoid TypeClassEnv where
   mempty =
     TypeClassEnv mempty mempty mempty
-  mappend (TypeClassEnv a1 b1 c1)
-          (TypeClassEnv a2 b2 c2) =
-    TypeClassEnv (a1 <> a2) (b1 <> b2) (c1 <> c2)
 
 -- |
 -- Take a TypeClassEnv and handle all of the type class members in it, either
diff --git a/src/Language/PureScript/Docs/Convert/Single.hs b/src/Language/PureScript/Docs/Convert/Single.hs
--- a/src/Language/PureScript/Docs/Convert/Single.hs
+++ b/src/Language/PureScript/Docs/Convert/Single.hs
@@ -114,7 +114,7 @@
 convertDeclaration (P.ValueDecl sa _ _ _ _) title =
   -- If no explicit type declaration was provided, insert a wildcard, so that
   -- the actual type will be added during type checking.
-  basicDeclaration sa title (ValueDeclaration P.TypeWildcard{})
+  basicDeclaration sa title (ValueDeclaration (P.TypeWildcard (fst sa)))
 convertDeclaration (P.ExternDeclaration sa _ ty) title =
   basicDeclaration sa title (ValueDeclaration ty)
 convertDeclaration (P.DataDeclaration sa dtype _ args ctors) title =
diff --git a/src/Language/PureScript/Docs/Prim.hs b/src/Language/PureScript/Docs/Prim.hs
--- a/src/Language/PureScript/Docs/Prim.hs
+++ b/src/Language/PureScript/Docs/Prim.hs
@@ -7,7 +7,6 @@
   ) where
 
 import Prelude.Compat hiding (fail)
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 import qualified Data.Map as Map
@@ -106,6 +105,7 @@
       , kindDoc
       , textDoc
       , quoteDoc
+      , quoteLabelDoc
       , besideDoc
       , aboveDoc
       ]
@@ -442,7 +442,7 @@
   [ "`Doc` is the kind of type-level documents."
   , ""
   , "This kind is used with the `Fail` and `Warn` type clases."
-  , "Build up a `Doc` with `Text`, `Quote`, `Beside`, and `Above`."
+  , "Build up a `Doc` with `Text`, `Quote`, `QuoteLabel`, `Beside`, and `Above`."
   ]
 
 textDoc :: Declaration
@@ -458,6 +458,15 @@
 quoteDoc = primTypeOf (P.primSubName "TypeError") "Quote" $ T.unlines
   [ "The Quote type constructor renders any concrete type as a Doc"
   , "to be used in a custom type error."
+  , ""
+  , "For more information, see"
+  , "[the Custom Type Errors guide](https://github.com/purescript/documentation/blob/master/guides/Custom-Type-Errors.md)."
+  ]
+
+quoteLabelDoc :: Declaration
+quoteLabelDoc = primTypeOf (P.primSubName "TypeError") "QuoteLabel" $ T.unlines
+  [ "The `QuoteLabel` type constructor will produce a `Doc` when given a `Symbol`. When the resulting `Doc` is rendered"
+  , "for a `Warn` or `Fail` constraint, a syntactically valid label will be produced, escaping with quotes as needed."
   , ""
   , "For more information, see"
   , "[the Custom Type Errors guide](https://github.com/purescript/documentation/blob/master/guides/Custom-Type-Errors.md)."
diff --git a/src/Language/PureScript/Docs/Render.hs b/src/Language/PureScript/Docs/Render.hs
--- a/src/Language/PureScript/Docs/Render.hs
+++ b/src/Language/PureScript/Docs/Render.hs
@@ -12,7 +12,6 @@
 import Prelude.Compat
 
 import Data.Maybe (maybeToList)
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 
diff --git a/src/Language/PureScript/Docs/RenderedCode/RenderKind.hs b/src/Language/PureScript/Docs/RenderedCode/RenderKind.hs
--- a/src/Language/PureScript/Docs/RenderedCode/RenderKind.hs
+++ b/src/Language/PureScript/Docs/RenderedCode/RenderKind.hs
@@ -12,7 +12,6 @@
 import Control.Arrow (ArrowPlus(..))
 import Control.PatternArrows as PA
 
-import Data.Monoid ((<>))
 import Data.Maybe (fromMaybe)
 import qualified Data.Text as T
 
diff --git a/src/Language/PureScript/Docs/RenderedCode/RenderType.hs b/src/Language/PureScript/Docs/RenderedCode/RenderType.hs
--- a/src/Language/PureScript/Docs/RenderedCode/RenderType.hs
+++ b/src/Language/PureScript/Docs/RenderedCode/RenderType.hs
@@ -13,7 +13,6 @@
 import Prelude.Compat
 
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import Data.Text (Text)
 
 import Control.Arrow ((<+>))
diff --git a/src/Language/PureScript/Docs/RenderedCode/Types.hs b/src/Language/PureScript/Docs/RenderedCode/Types.hs
--- a/src/Language/PureScript/Docs/RenderedCode/Types.hs
+++ b/src/Language/PureScript/Docs/RenderedCode/Types.hs
@@ -49,7 +49,6 @@
 import Control.DeepSeq (NFData)
 import Control.Monad.Error.Class (MonadError(..))
 
-import Data.Monoid ((<>))
 import Data.Aeson.BetterErrors (Parse, nth, withText, withValue, toAesonParser, perhaps, asText, eachInArray)
 import qualified Data.Aeson as A
 import Data.Text (Text)
@@ -248,7 +247,7 @@
 --
 newtype RenderedCode
   = RC { unRC :: [RenderedCodeElement] }
-  deriving (Show, Eq, Ord, Monoid)
+  deriving (Show, Eq, Ord, Semigroup, Monoid)
 
 instance A.ToJSON RenderedCode where
   toJSON (RC elems) = A.toJSON elems
diff --git a/src/Language/PureScript/Docs/Utils/MonoidExtras.hs b/src/Language/PureScript/Docs/Utils/MonoidExtras.hs
--- a/src/Language/PureScript/Docs/Utils/MonoidExtras.hs
+++ b/src/Language/PureScript/Docs/Utils/MonoidExtras.hs
@@ -6,4 +6,3 @@
 mintersperse _ []       = mempty
 mintersperse _ [x]      = x
 mintersperse sep (x:xs) = x <> sep <> mintersperse sep xs
-
diff --git a/src/Language/PureScript/Environment.hs b/src/Language/PureScript/Environment.hs
--- a/src/Language/PureScript/Environment.hs
+++ b/src/Language/PureScript/Environment.hs
@@ -449,6 +449,7 @@
     , (primSubName C.typeError "Warn", (kindDoc -:> kindConstraint, ExternData))
     , (primSubName C.typeError "Text", (kindSymbol -:> kindDoc, ExternData))
     , (primSubName C.typeError "Quote", (kindType -:> kindDoc, ExternData))
+    , (primSubName C.typeError "QuoteLabel", (kindSymbol -:> kindDoc, ExternData))
     , (primSubName C.typeError "Beside", (kindDoc -:> kindDoc -:> kindDoc, ExternData))
     , (primSubName C.typeError "Above", (kindDoc -:> kindDoc -:> kindDoc, ExternData))
     ]
diff --git a/src/Language/PureScript/Errors.hs b/src/Language/PureScript/Errors.hs
--- a/src/Language/PureScript/Errors.hs
+++ b/src/Language/PureScript/Errors.hs
@@ -186,7 +186,7 @@
 -- | A stack trace for an error
 newtype MultipleErrors = MultipleErrors
   { runMultipleErrors :: [ErrorMessage]
-  } deriving (Show, Monoid)
+  } deriving (Show, Semigroup, Monoid)
 
 -- | Check whether a collection of errors is empty or not.
 nonEmpty :: MultipleErrors -> Bool
@@ -753,8 +753,12 @@
       line $ "Argument list lengths differ in declaration " <> markCode (showIdent ident)
     renderSimpleErrorMessage (OverlappingArgNames ident) =
       line $ "Overlapping names in function/binder" <> foldMap ((" in declaration " <>) . showIdent) ident
-    renderSimpleErrorMessage (MissingClassMember ident) =
-      line $ "Type class member " <> markCode (showIdent ident) <> " has not been implemented."
+    renderSimpleErrorMessage (MissingClassMember identsAndTypes) =
+      paras $ [ line "The following type class members have not been implemented:"
+              , Box.vcat Box.left
+                [ markCodeBox $ Box.text (T.unpack (showIdent ident)) Box.<> " :: " Box.<> typeAsBox ty
+                | (ident, ty) <- NEL.toList identsAndTypes ]
+              ]
     renderSimpleErrorMessage (ExtraneousClassMember ident className) =
       line $ "" <> markCode (showIdent ident) <> " is not a member of type class " <> markCode (showQualified runProperName className)
     renderSimpleErrorMessage (ExpectedType ty kind) =
@@ -1405,6 +1409,8 @@
   | f == primSubName C.typeError "Text" = toTypelevelString x
 toTypelevelString (TypeApp (TypeConstructor f) x)
   | f == primSubName C.typeError "Quote" = Just (typeAsBox x)
+toTypelevelString (TypeApp (TypeConstructor f) (TypeLevelString x))
+  | f == primSubName C.typeError "QuoteLabel" = Just . line . prettyPrintLabel . Label $ x
 toTypelevelString (TypeApp (TypeApp (TypeConstructor f) x) ret)
   | f == primSubName C.typeError "Beside" =
     (Box.<>) <$> toTypelevelString x <*> toTypelevelString ret
diff --git a/src/Language/PureScript/Errors/JSON.hs b/src/Language/PureScript/Errors/JSON.hs
--- a/src/Language/PureScript/Errors/JSON.hs
+++ b/src/Language/PureScript/Errors/JSON.hs
@@ -6,7 +6,6 @@
 
 import qualified Data.Aeson.TH as A
 import qualified Data.List.NonEmpty as NEL
-import Data.Monoid ((<>))
 import qualified Data.Text as T
 import Data.Text (Text)
 
diff --git a/src/Language/PureScript/Hierarchy.hs b/src/Language/PureScript/Hierarchy.hs
--- a/src/Language/PureScript/Hierarchy.hs
+++ b/src/Language/PureScript/Hierarchy.hs
@@ -19,7 +19,6 @@
 import           Protolude (ordNub)
 
 import           Data.List (sort)
-import           Data.Monoid ((<>))
 import qualified Data.Text as T
 import qualified Language.PureScript as P
 
diff --git a/src/Language/PureScript/Ide.hs b/src/Language/PureScript/Ide.hs
--- a/src/Language/PureScript/Ide.hs
+++ b/src/Language/PureScript/Ide.hs
@@ -94,10 +94,10 @@
       Right rs' -> answerRequest outfp rs'
       Left question ->
         pure (CompletionResult (map (completionFromMatch . simpleExport . map withEmptyAnn) question))
-  Rebuild file actualFile ->
-    rebuildFileAsync file actualFile
-  RebuildSync file actualFile ->
-    rebuildFileSync file actualFile
+  Rebuild file actualFile targets ->
+    rebuildFileAsync file actualFile targets
+  RebuildSync file actualFile targets ->
+    rebuildFileSync file actualFile targets
   Cwd ->
     TextResult . T.pack <$> liftIO getCurrentDirectory
   Reset ->
diff --git a/src/Language/PureScript/Ide/Command.hs b/src/Language/PureScript/Ide/Command.hs
--- a/src/Language/PureScript/Ide/Command.hs
+++ b/src/Language/PureScript/Ide/Command.hs
@@ -17,6 +17,8 @@
 import           Protolude
 
 import           Data.Aeson
+import qualified Data.Map as Map
+import qualified Data.Set as Set
 import qualified Language.PureScript               as P
 import           Language.PureScript.Ide.CaseSplit
 import           Language.PureScript.Ide.Completion
@@ -57,8 +59,8 @@
       -- Import InputFile OutputFile
     | Import FilePath (Maybe FilePath) [Filter] ImportCommand
     | List { listType :: ListType }
-    | Rebuild FilePath (Maybe FilePath)
-    | RebuildSync FilePath (Maybe FilePath)
+    | Rebuild FilePath (Maybe FilePath) (Set P.CodegenTarget)
+    | RebuildSync FilePath (Maybe FilePath) (Set P.CodegenTarget)
     | Cwd
     | Reset
     | Quit
@@ -172,7 +174,11 @@
         Rebuild
           <$> params .: "file"
           <*> params .:? "actualFile"
+          <*> (parseCodegenTargets =<< params .:? "codegen" .!= [ "js" ])
       _ -> mzero
     where
+      parseCodegenTargets =
+        maybe mzero (pure . Set.fromList) . traverse (flip Map.lookup P.codegenTargets)
+
       mkAnnotations True = explicitAnnotations
       mkAnnotations False = noAnnotations
diff --git a/src/Language/PureScript/Ide/Completion.hs b/src/Language/PureScript/Ide/Completion.hs
--- a/src/Language/PureScript/Ide/Completion.hs
+++ b/src/Language/PureScript/Ide/Completion.hs
@@ -11,7 +11,6 @@
 
 import           Protolude hiding ((<&>), moduleName)
 
-import           Control.Lens hiding ((&), op)
 import           Data.Aeson
 import qualified Data.Map as Map
 import qualified Data.Text as T
@@ -21,6 +20,7 @@
 import           Language.PureScript.Ide.Matcher
 import           Language.PureScript.Ide.Types
 import           Language.PureScript.Ide.Util
+import           Lens.Micro.Platform hiding ((&))
 
 type Module = (P.ModuleName, [IdeDeclarationAnn])
 
diff --git a/src/Language/PureScript/Ide/Externs.hs b/src/Language/PureScript/Ide/Externs.hs
--- a/src/Language/PureScript/Ide/Externs.hs
+++ b/src/Language/PureScript/Ide/Externs.hs
@@ -21,7 +21,6 @@
 
 import           Protolude hiding (to, from, (&))
 
-import           Control.Lens
 import           "monad-logger" Control.Monad.Logger
 import           Data.Aeson (decodeStrict)
 import           Data.Aeson.Types (withObject, parseMaybe, (.:))
@@ -29,6 +28,7 @@
 import           Data.Version (showVersion)
 import           Language.PureScript.Ide.Error (IdeError (..))
 import           Language.PureScript.Ide.Types
+import           Lens.Micro.Platform
 
 import qualified Language.PureScript as P
 
diff --git a/src/Language/PureScript/Ide/Filter.hs b/src/Language/PureScript/Ide/Filter.hs
--- a/src/Language/PureScript/Ide/Filter.hs
+++ b/src/Language/PureScript/Ide/Filter.hs
@@ -35,7 +35,7 @@
 import qualified Language.PureScript           as P
 
 newtype Filter = Filter (Endo [Module])
-  deriving (Monoid)
+  deriving (Semigroup, Monoid)
 
 type Module = (P.ModuleName, [IdeDeclarationAnn])
 
diff --git a/src/Language/PureScript/Ide/Imports.hs b/src/Language/PureScript/Ide/Imports.hs
--- a/src/Language/PureScript/Ide/Imports.hs
+++ b/src/Language/PureScript/Ide/Imports.hs
@@ -32,7 +32,6 @@
 
 import           Protolude hiding (moduleName)
 
-import           Control.Lens                       ((^.), (%~), ix)
 import           Data.List                          (findIndex, nubBy, partition)
 import qualified Data.Map                           as Map
 import qualified Data.Text                          as T
@@ -45,6 +44,7 @@
 import           Language.PureScript.Ide.Prim
 import           Language.PureScript.Ide.Types
 import           Language.PureScript.Ide.Util
+import           Lens.Micro.Platform                ((^.), (%~), ix)
 import           System.IO.UTF8                     (writeUTF8FileT)
 import qualified Text.Parsec as Parsec
 
diff --git a/src/Language/PureScript/Ide/Matcher.hs b/src/Language/PureScript/Ide/Matcher.hs
--- a/src/Language/PureScript/Ide/Matcher.hs
+++ b/src/Language/PureScript/Ide/Matcher.hs
@@ -35,7 +35,7 @@
 
 type ScoredMatch a = (Match a, Double)
 
-newtype Matcher a = Matcher (Endo [Match a]) deriving (Monoid)
+newtype Matcher a = Matcher (Endo [Match a]) deriving (Semigroup, Monoid)
 
 instance FromJSON (Matcher IdeDeclarationAnn) where
   parseJSON = withObject "matcher" $ \o -> do
diff --git a/src/Language/PureScript/Ide/Rebuild.hs b/src/Language/PureScript/Ide/Rebuild.hs
--- a/src/Language/PureScript/Ide/Rebuild.hs
+++ b/src/Language/PureScript/Ide/Rebuild.hs
@@ -42,10 +42,12 @@
   -- ^ The file to rebuild
   -> Maybe FilePath
   -- ^ The file to use as the location for parsing and errors
+  -> Set P.CodegenTarget
+  -- ^ The targets to codegen
   -> (ReaderT IdeEnvironment (LoggingT IO) () -> m ())
   -- ^ A runner for the second build with open exports
   -> m Success
-rebuildFile file actualFile runOpenBuild = do
+rebuildFile file actualFile codegenTargets runOpenBuild = do
 
   input <- ideReadFile file
 
@@ -69,7 +71,7 @@
   -- Rebuild the single module using the cached externs
   (result, warnings) <- logPerf (labelTimespec "Rebuilding Module") $
     liftIO
-    . P.runMake P.defaultOptions
+    . P.runMake (P.defaultOptions { P.optionsCodegenTargets = codegenTargets })
     . P.rebuildModule (buildMakeActions
                         >>= shushProgress $ makeEnv) externs $ m
   case result of
@@ -87,8 +89,8 @@
 
 rebuildFileAsync
   :: forall m. (Ide m, MonadLogger m, MonadError IdeError m)
-  => FilePath -> Maybe FilePath -> m Success
-rebuildFileAsync fp fp' = rebuildFile fp fp' asyncRun
+  => FilePath -> Maybe FilePath -> Set P.CodegenTarget -> m Success
+rebuildFileAsync fp fp' ts = rebuildFile fp fp' ts asyncRun
   where
     asyncRun :: ReaderT IdeEnvironment (LoggingT IO) () -> m ()
     asyncRun action = do
@@ -98,8 +100,8 @@
 
 rebuildFileSync
   :: forall m. (Ide m, MonadLogger m, MonadError IdeError m)
-  => FilePath -> Maybe FilePath -> m Success
-rebuildFileSync fp fp' = rebuildFile fp fp' syncRun
+  => FilePath -> Maybe FilePath -> Set P.CodegenTarget -> m Success
+rebuildFileSync fp fp' ts = rebuildFile fp fp' ts syncRun
   where
     syncRun :: ReaderT IdeEnvironment (LoggingT IO) () -> m ()
     syncRun action = do
@@ -154,11 +156,12 @@
 shushProgress ma _ =
   ma { P.progress = \_ -> pure () }
 
--- | Stops any kind of codegen (also silences errors about missing or unused FFI
--- files though)
+-- | Stops any kind of codegen
 shushCodegen :: P.MakeActions P.Make -> MakeActionsEnv -> P.MakeActions P.Make
 shushCodegen ma MakeActionsEnv{..} =
-  ma { P.codegen = \_ _ _ -> pure () }
+  ma { P.codegen = \_ _ _ -> pure ()
+     , P.ffiCodegen = \_ -> pure ()
+     }
 
 -- | Returns a topologically sorted list of dependent ExternsFiles for the given
 -- module. Throws an error if there is a cyclic dependency within the
diff --git a/src/Language/PureScript/Ide/Reexports.hs b/src/Language/PureScript/Ide/Reexports.hs
--- a/src/Language/PureScript/Ide/Reexports.hs
+++ b/src/Language/PureScript/Ide/Reexports.hs
@@ -25,11 +25,11 @@
 
 import           Protolude hiding (moduleName)
 
-import           Control.Lens                  hiding ((&))
 import qualified Data.Map                      as Map
 import qualified Language.PureScript           as P
 import           Language.PureScript.Ide.Types
 import           Language.PureScript.Ide.Util
+import           Lens.Micro.Platform           hiding ((&))
 
 -- | Contains the module with resolved reexports, and possible failures
 data ReexportResult a
diff --git a/src/Language/PureScript/Ide/State.hs b/src/Language/PureScript/Ide/State.hs
--- a/src/Language/PureScript/Ide/State.hs
+++ b/src/Language/PureScript/Ide/State.hs
@@ -41,7 +41,6 @@
 
 import           Control.Arrow
 import           Control.Concurrent.STM
-import           Control.Lens                       hiding (op, (&))
 import           "monad-logger" Control.Monad.Logger
 import qualified Data.Map.Lazy                      as Map
 import qualified Language.PureScript                as P
@@ -52,6 +51,7 @@
 import           Language.PureScript.Ide.SourceFile
 import           Language.PureScript.Ide.Types
 import           Language.PureScript.Ide.Util
+import           Lens.Micro.Platform                hiding ((&))
 
 -- | Resets all State inside psc-ide
 resetIdeState :: Ide m => m ()
@@ -329,7 +329,7 @@
           mapIf matchTC (idaDeclaration
                          . _IdeDeclTypeClass
                          . ideTCInstances
-                         %~ cons ideInstance)
+                         %~ (ideInstance :))
       in
         acc' & ix classModule %~ updateDeclaration
 
diff --git a/src/Language/PureScript/Ide/Types.hs b/src/Language/PureScript/Ide/Types.hs
--- a/src/Language/PureScript/Ide/Types.hs
+++ b/src/Language/PureScript/Ide/Types.hs
@@ -22,11 +22,11 @@
 import           Protolude hiding (moduleName)
 
 import           Control.Concurrent.STM
-import           Control.Lens.TH
 import           Data.Aeson
 import qualified Data.Map.Lazy as M
 import qualified Language.PureScript as P
 import qualified Language.PureScript.Errors.JSON as P
+import           Lens.Micro.Platform hiding ((.=))
 
 type ModuleIdent = Text
 type ModuleMap a = Map P.ModuleName a
@@ -94,7 +94,41 @@
   , _ideTypeOpKind          :: Maybe P.Kind
   } deriving (Show, Eq, Ord, Generic, NFData)
 
-makePrisms ''IdeDeclaration
+_IdeDeclValue :: Traversal' IdeDeclaration IdeValue
+_IdeDeclValue f (IdeDeclValue x) = map IdeDeclValue (f x)
+_IdeDeclValue _ x = pure x
+
+_IdeDeclType :: Traversal' IdeDeclaration IdeType
+_IdeDeclType f (IdeDeclType x) = map IdeDeclType (f x)
+_IdeDeclType _ x = pure x
+
+_IdeDeclTypeSynonym :: Traversal' IdeDeclaration IdeTypeSynonym
+_IdeDeclTypeSynonym f (IdeDeclTypeSynonym x) = map IdeDeclTypeSynonym (f x)
+_IdeDeclTypeSynonym _ x = pure x
+
+_IdeDeclDataConstructor :: Traversal' IdeDeclaration IdeDataConstructor
+_IdeDeclDataConstructor f (IdeDeclDataConstructor x) = map IdeDeclDataConstructor (f x)
+_IdeDeclDataConstructor _ x = pure x
+
+_IdeDeclTypeClass :: Traversal' IdeDeclaration IdeTypeClass
+_IdeDeclTypeClass f (IdeDeclTypeClass x) = map IdeDeclTypeClass (f x)
+_IdeDeclTypeClass _ x = pure x
+
+_IdeDeclValueOperator :: Traversal' IdeDeclaration IdeValueOperator
+_IdeDeclValueOperator f (IdeDeclValueOperator x) = map IdeDeclValueOperator (f x)
+_IdeDeclValueOperator _ x = pure x
+
+_IdeDeclTypeOperator :: Traversal' IdeDeclaration IdeTypeOperator
+_IdeDeclTypeOperator f (IdeDeclTypeOperator x) = map IdeDeclTypeOperator (f x)
+_IdeDeclTypeOperator _ x = pure x
+
+_IdeDeclKind :: Traversal' IdeDeclaration (P.ProperName 'P.KindName)
+_IdeDeclKind f (IdeDeclKind x) = map IdeDeclKind (f x)
+_IdeDeclKind _ x = pure x
+
+anyOf :: Getting Any s a -> (a -> Bool) -> s -> Bool
+anyOf g p = getAny . getConst . g (Const . Any . p)
+
 makeLenses ''IdeValue
 makeLenses ''IdeType
 makeLenses ''IdeTypeSynonym
diff --git a/src/Language/PureScript/Ide/Usage.hs b/src/Language/PureScript/Ide/Usage.hs
--- a/src/Language/PureScript/Ide/Usage.hs
+++ b/src/Language/PureScript/Ide/Usage.hs
@@ -8,13 +8,13 @@
 
 import           Protolude hiding (moduleName)
 
-import           Control.Lens (preview)
 import qualified Data.Map as Map
 import qualified Data.Set as Set
 import qualified Language.PureScript as P
 import           Language.PureScript.Ide.State (getAllModules, getFileState)
 import           Language.PureScript.Ide.Types
 import           Language.PureScript.Ide.Util
+import           Lens.Micro.Platform (preview)
 
 -- |
 -- How we find usages, given an IdeDeclaration and the module it was defined in:
diff --git a/src/Language/PureScript/Ide/Util.hs b/src/Language/PureScript/Ide/Util.hs
--- a/src/Language/PureScript/Ide/Util.hs
+++ b/src/Language/PureScript/Ide/Util.hs
@@ -30,9 +30,8 @@
   ) where
 
 import           Protolude                           hiding (decodeUtf8,
-                                                      encodeUtf8)
+                                                      encodeUtf8, to)
 
-import           Control.Lens                        hiding ((&), op)
 import           Data.Aeson
 import qualified Data.Text.Lazy                      as TL
 import           Data.Text.Lazy.Encoding             as TLE
@@ -40,6 +39,7 @@
 import           Language.PureScript.Ide.Error       (IdeError(..))
 import           Language.PureScript.Ide.Logging
 import           Language.PureScript.Ide.Types
+import           Lens.Micro.Platform                 hiding ((&))
 import           System.IO.UTF8                      (readUTF8FileT)
 import           System.Directory                    (makeAbsolute)
 
@@ -90,14 +90,14 @@
 decodeT :: (FromJSON a) => Text -> Maybe a
 decodeT = decode . TLE.encodeUtf8 . TL.fromStrict
 
-properNameT :: Iso' (P.ProperName a) Text
-properNameT = iso P.runProperName P.ProperName
+properNameT :: Getting r (P.ProperName a) Text
+properNameT = to P.runProperName
 
-identT :: Iso' P.Ident Text
-identT = iso P.runIdent P.Ident
+identT :: Getting r P.Ident Text
+identT = to P.runIdent
 
-opNameT :: Iso' (P.OpName a) Text
-opNameT = iso P.runOpName P.OpName
+opNameT :: Getting r (P.OpName a) Text
+opNameT = to P.runOpName
 
 ideReadFile'
   :: (MonadIO m, MonadError IdeError m)
diff --git a/src/Language/PureScript/Interactive.hs b/src/Language/PureScript/Interactive.hs
--- a/src/Language/PureScript/Interactive.hs
+++ b/src/Language/PureScript/Interactive.hs
@@ -16,7 +16,6 @@
 import           Data.List (sort, find, foldl')
 import           Data.Maybe (fromMaybe, mapMaybe)
 import qualified Data.Map as M
-import           Data.Monoid ((<>))
 import qualified Data.Set as S
 import           Data.Text (Text)
 import qualified Data.Text as T
@@ -292,7 +291,7 @@
   -> m ()
 handleBrowse print' moduleName = do
   st <- get
-  env <- asks psciEnvironment
+  let env = psciEnvironment st
   case findMod moduleName (psciLoadedExterns st) (psciImportedModules st) of
     Just qualName -> print' $ printModuleSignatures qualName env
     Nothing       -> failNotInEnv moduleName
diff --git a/src/Language/PureScript/Interactive/Printer.hs b/src/Language/PureScript/Interactive/Printer.hs
--- a/src/Language/PureScript/Interactive/Printer.hs
+++ b/src/Language/PureScript/Interactive/Printer.hs
@@ -5,7 +5,6 @@
 import           Data.List (intersperse)
 import qualified Data.Map as M
 import           Data.Maybe (mapMaybe)
-import           Data.Monoid ((<>))
 import qualified Data.Text as T
 import           Data.Text (Text)
 import qualified Language.PureScript as P
diff --git a/src/Language/PureScript/Interactive/Types.hs b/src/Language/PureScript/Interactive/Types.hs
--- a/src/Language/PureScript/Interactive/Types.hs
+++ b/src/Language/PureScript/Interactive/Types.hs
@@ -3,6 +3,7 @@
 --
 module Language.PureScript.Interactive.Types
   ( PSCiConfig(..)
+  , psciEnvironment
   , PSCiState -- constructor is not exported, to prevent psciImports and psciExports from
               -- becoming inconsistent with importedModules, letBindings and loadedExterns
   , ImportedModule
@@ -29,6 +30,7 @@
 
 import qualified Language.PureScript as P
 import qualified Data.Map as M
+import           Data.List (foldl')
 import           Language.PureScript.Sugar.Names.Env (nullImports, primExports)
 import           Control.Monad.Trans.Except (runExceptT)
 import           Control.Monad.Writer.Strict (runWriterT)
@@ -38,9 +40,8 @@
 --
 -- These configuration values do not change during execution.
 --
-data PSCiConfig = PSCiConfig
-  { psciFileGlobs           :: [String]
-  , psciEnvironment         :: P.Environment
+newtype PSCiConfig = PSCiConfig
+  { psciFileGlobs :: [String]
   } deriving Show
 
 -- | The PSCI state.
@@ -78,6 +79,10 @@
 initialPSCiState :: PSCiState
 initialPSCiState = PSCiState [] [] [] nullImports primExports
 
+psciEnvironment :: PSCiState -> P.Environment
+psciEnvironment st = foldl' (flip P.applyExternsFileToEnvironment) P.initEnvironment externs
+  where externs = map snd (psciLoadedExterns st)
+
 -- | All of the data that is contained by an ImportDeclaration in the AST.
 -- That is:
 --
@@ -137,7 +142,7 @@
 -- | Updates the loaded externs files in the state record.
 updateLoadedExterns :: ([(P.Module, P.ExternsFile)] -> [(P.Module, P.ExternsFile)]) -> PSCiState -> PSCiState
 updateLoadedExterns f (PSCiState a b x c d) =
-  PSCiState a b (f x) c d
+  updateImportExports (PSCiState a b (f x) c d)
 
 -- | Updates the let bindings in the state record.
 updateLets :: ([P.Declaration] -> [P.Declaration]) -> PSCiState -> PSCiState
diff --git a/src/Language/PureScript/Kinds.hs b/src/Language/PureScript/Kinds.hs
--- a/src/Language/PureScript/Kinds.hs
+++ b/src/Language/PureScript/Kinds.hs
@@ -102,8 +102,8 @@
   go other = f other
 
 everythingOnKinds :: (r -> r -> r) -> (Kind -> r) -> Kind -> r
-everythingOnKinds (<>) f = go
+everythingOnKinds (<>.) f = go
   where
-  go k@(Row k1) = f k <> go k1
-  go k@(FunKind k1 k2) = f k <> go k1 <> go k2
+  go k@(Row k1) = f k <>. go k1
+  go k@(FunKind k1 k2) = f k <>. go k1 <>. go k2
   go other = f other
diff --git a/src/Language/PureScript/Label.hs b/src/Language/PureScript/Label.hs
--- a/src/Language/PureScript/Label.hs
+++ b/src/Language/PureScript/Label.hs
@@ -17,6 +17,6 @@
 -- because records are indexable by PureScript strings at runtime.
 --
 newtype Label = Label { runLabel :: PSString }
-  deriving (Show, Eq, Ord, IsString, Monoid, A.ToJSON, A.FromJSON, Generic)
+  deriving (Show, Eq, Ord, IsString, Semigroup, Monoid, A.ToJSON, A.FromJSON, Generic)
 
 instance NFData Label
diff --git a/src/Language/PureScript/Linter.hs b/src/Language/PureScript/Linter.hs
--- a/src/Language/PureScript/Linter.hs
+++ b/src/Language/PureScript/Linter.hs
@@ -10,7 +10,6 @@
 
 import Data.List ((\\))
 import Data.Maybe (mapMaybe)
-import Data.Monoid
 import qualified Data.Set as S
 import Data.Text (Text)
 
diff --git a/src/Language/PureScript/Linter/Exhaustive.hs b/src/Language/PureScript/Linter/Exhaustive.hs
--- a/src/Language/PureScript/Linter/Exhaustive.hs
+++ b/src/Language/PureScript/Linter/Exhaustive.hs
@@ -20,7 +20,6 @@
 import Data.Function (on)
 import Data.List (foldl', sortBy)
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import qualified Data.Map as M
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/src/Language/PureScript/Make.hs b/src/Language/PureScript/Make.hs
--- a/src/Language/PureScript/Make.hs
+++ b/src/Language/PureScript/Make.hs
@@ -75,6 +75,7 @@
       optimized = CF.optimizeCoreFn corefn
       [renamed] = renameInModules [optimized]
       exts = moduleToExternsFile mod' env'
+  ffiCodegen renamed
   evalSupplyT nextVar' . codegen renamed env' . encode $ exts
   return exts
 
diff --git a/src/Language/PureScript/Make/Actions.hs b/src/Language/PureScript/Make/Actions.hs
--- a/src/Language/PureScript/Make/Actions.hs
+++ b/src/Language/PureScript/Make/Actions.hs
@@ -4,6 +4,7 @@
   , Externs()
   , ProgressMessage(..)
   , buildMakeActions
+  , checkForeignDecls
   ) where
 
 import           Prelude
@@ -18,13 +19,12 @@
 import           Data.Aeson (encode)
 import qualified Data.ByteString.Lazy as B
 import qualified Data.ByteString.Lazy as LB
-import qualified Data.ByteString.UTF8 as BU8
+import qualified Data.ByteString.Lazy.UTF8 as LBU8
 import           Data.Either (partitionEithers)
 import           Data.Foldable (for_, minimum)
 import qualified Data.List.NonEmpty as NEL
 import qualified Data.Map as M
 import           Data.Maybe (fromMaybe)
-import           Data.Monoid ((<>))
 import qualified Data.Set as S
 import qualified Data.Text as T
 import qualified Data.Text.Encoding as TE
@@ -44,7 +44,7 @@
 import           Language.PureScript.Make.Monad
 import           Language.PureScript.Names
 import           Language.PureScript.Names (runModuleName, ModuleName)
-import           Language.PureScript.Options
+import           Language.PureScript.Options hiding (codegenTargets)
 import qualified Language.PureScript.Parser as PSParser
 import           Language.PureScript.Pretty.Common (SMap(..))
 import qualified Paths_purescript as Paths
@@ -96,6 +96,8 @@
   -- path for the file.
   , codegen :: CF.Module CF.Ann -> Environment -> Externs -> SupplyT m ()
   -- ^ Run the code generator for the module and write any required output files.
+  , ffiCodegen :: CF.Module CF.Ann -> m ()
+  -- ^ Check ffi and print it in the output directory.
   , progress :: ProgressMessage -> m ()
   -- ^ Respond to a progress update.
   }
@@ -112,7 +114,7 @@
   -- ^ Generate a prefix comment?
   -> MakeActions Make
 buildMakeActions outputDir filePathMap foreigns usePrefix =
-    MakeActions getInputTimestamp getOutputTimestamp readExterns codegen progress
+    MakeActions getInputTimestamp getOutputTimestamp readExterns codegen ffiCodegen progress
   where
 
   getInputTimestamp :: ModuleName -> Make (Either RebuildPolicy (Maybe UTCTime))
@@ -156,12 +158,10 @@
       lift $ writeTextFile coreFnFile (encode json)
     when (S.member JS codegenTargets) $ do
       foreignInclude <- case mn `M.lookup` foreigns of
-        Just path
+        Just _
           | not $ requiresForeign m -> do
-              tell $ errorMessage' (CF.moduleSourceSpan m) $ UnnecessaryFFIModule mn path
               return Nothing
           | otherwise -> do
-              checkForeignDecls m path
               return $ Just $ Imp.App Nothing (Imp.Var Nothing "require") [Imp.StringLiteral Nothing "./foreign.js"]
         Nothing | requiresForeign m -> throwError . errorMessage' (CF.moduleSourceSpan m) $ MissingFFIModule mn
                 | otherwise -> return Nothing
@@ -169,7 +169,6 @@
       dir <- lift $ makeIO (const (ErrorMessage [] $ CannotGetFileInfo ".")) getCurrentDirectory
       let sourceMaps = S.member JSSourceMap codegenTargets
           (pjs, mappings) = if sourceMaps then prettyPrintJSWithSourceMaps rawJs else (prettyPrintJS rawJs, [])
-          foreignFile = outputFilename mn "foreign.js"
           jsFile = targetFilename mn JS
           mapFile = targetFilename mn JSSourceMap
           prefix = ["Generated by purs version " <> T.pack (showVersion Paths.version) | usePrefix]
@@ -177,9 +176,24 @@
           mapRef = if sourceMaps then "//# sourceMappingURL=index.js.map\n" else ""
       lift $ do
         writeTextFile jsFile (B.fromStrict $ TE.encodeUtf8 $ js <> mapRef)
-        for_ (mn `M.lookup` foreigns) (readTextFile >=> writeTextFile foreignFile)
         when sourceMaps $ genSourceMap dir mapFile (length prefix) mappings
 
+  ffiCodegen :: CF.Module CF.Ann -> Make ()
+  ffiCodegen m = do
+    codegenTargets <- asks optionsCodegenTargets
+    when (S.member JS codegenTargets) $ do
+      let mn = CF.moduleName m
+          foreignFile = outputFilename mn "foreign.js"
+      case mn `M.lookup` foreigns of
+        Just path
+          | not $ requiresForeign m ->
+              tell $ errorMessage' (CF.moduleSourceSpan m) $ UnnecessaryFFIModule mn path
+          | otherwise ->
+              checkForeignDecls m path
+        Nothing | requiresForeign m -> throwError . errorMessage' (CF.moduleSourceSpan m) $ MissingFFIModule mn
+                | otherwise -> return ()
+      for_ (mn `M.lookup` foreigns) (readTextFile >=> writeTextFile foreignFile)
+
   genSourceMap :: String -> String -> Int -> [SMap] -> Make ()
   genSourceMap dir mapFile extraLines mappings = do
     let pathToDir = iterate (".." </>) ".." !! length (splitPath $ normalise outputDir)
@@ -227,10 +241,10 @@
 
 -- | Check that the declarations in a given PureScript module match with those
 -- in its corresponding foreign module.
-checkForeignDecls :: CF.Module ann -> FilePath -> SupplyT Make ()
+checkForeignDecls :: CF.Module ann -> FilePath -> Make ()
 checkForeignDecls m path = do
-  jsStr <- lift $ readTextFile path
-  js <- either (errorParsingModule . Bundle.UnableToParseModule) pure $ JS.parse (BU8.toString (B.toStrict jsStr)) path
+  jsStr <- readTextFile path
+  js <- either (errorParsingModule . Bundle.UnableToParseModule) pure $ JS.parse (LBU8.toString jsStr) path
 
   foreignIdentsStrs <- either errorParsingModule pure $ getExps js
   foreignIdents <- either
@@ -253,13 +267,13 @@
   mname = CF.moduleName m
   modSS = CF.moduleSourceSpan m
 
-  errorParsingModule :: Bundle.ErrorMessage -> SupplyT Make a
+  errorParsingModule :: Bundle.ErrorMessage -> Make a
   errorParsingModule = throwError . errorMessage' modSS . ErrorParsingFFIModule path . Just
 
   getExps :: JS.JSAST -> Either Bundle.ErrorMessage [String]
   getExps = Bundle.getExportedIdentifiers (T.unpack (runModuleName mname))
 
-  errorInvalidForeignIdentifiers :: [String] -> SupplyT Make a
+  errorInvalidForeignIdentifiers :: [String] -> Make a
   errorInvalidForeignIdentifiers =
     throwError . mconcat . map (errorMessage . InvalidFFIIdentifier mname . T.pack)
 
diff --git a/src/Language/PureScript/Names.hs b/src/Language/PureScript/Names.hs
--- a/src/Language/PureScript/Names.hs
+++ b/src/Language/PureScript/Names.hs
@@ -16,7 +16,6 @@
 import GHC.Generics (Generic)
 import Data.Aeson
 import Data.Aeson.TH
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 
diff --git a/src/Language/PureScript/Options.hs b/src/Language/PureScript/Options.hs
--- a/src/Language/PureScript/Options.hs
+++ b/src/Language/PureScript/Options.hs
@@ -3,6 +3,8 @@
 
 import Prelude.Compat
 import qualified Data.Set as S
+import Data.Map (Map)
+import qualified Data.Map as Map
 
 -- | The data type of compiler options
 data Options = Options
@@ -20,3 +22,10 @@
 
 data CodegenTarget = JS | JSSourceMap | CoreFn
   deriving (Eq, Ord, Show)
+
+codegenTargets :: Map String CodegenTarget
+codegenTargets = Map.fromList
+  [ ("js", JS)
+  , ("sourcemaps", JSSourceMap)
+  , ("corefn", CoreFn)
+  ]
diff --git a/src/Language/PureScript/PSString.hs b/src/Language/PureScript/PSString.hs
--- a/src/Language/PureScript/PSString.hs
+++ b/src/Language/PureScript/PSString.hs
@@ -21,7 +21,6 @@
 import Data.Char (chr)
 import Data.Bits (shiftR)
 import Data.List (unfoldr)
-import Data.Monoid ((<>))
 import Data.Scientific (toBoundedInteger)
 import Data.String (IsString(..))
 import Data.ByteString (ByteString)
@@ -52,7 +51,7 @@
 -- and arrays of UTF-16 code units (integers) otherwise.
 --
 newtype PSString = PSString { toUTF16CodeUnits :: [Word16] }
-  deriving (Eq, Ord, Monoid, Generic)
+  deriving (Eq, Ord, Semigroup, Monoid, Generic)
 
 instance NFData PSString
 
diff --git a/src/Language/PureScript/Parser/Common.hs b/src/Language/PureScript/Parser/Common.hs
--- a/src/Language/PureScript/Parser/Common.hs
+++ b/src/Language/PureScript/Parser/Common.hs
@@ -6,7 +6,6 @@
 import           Control.Applicative ((<|>))
 import           Control.Monad (guard)
 import           Data.Maybe (fromMaybe)
-import           Data.Monoid ((<>))
 import           Data.Text (Text)
 import qualified Data.Text as T
 import           Language.PureScript.AST.SourcePos
diff --git a/src/Language/PureScript/Parser/Declarations.hs b/src/Language/PureScript/Parser/Declarations.hs
--- a/src/Language/PureScript/Parser/Declarations.hs
+++ b/src/Language/PureScript/Parser/Declarations.hs
@@ -25,7 +25,6 @@
 import           Control.Parallel.Strategies (withStrategy, parList, rseq)
 import           Data.Functor (($>))
 import           Data.Maybe (fromMaybe)
-import           Data.Monoid ((<>))
 import qualified Data.Set as S
 import           Data.Text (Text)
 import           Language.PureScript.AST
diff --git a/src/Language/PureScript/Parser/Lexer.hs b/src/Language/PureScript/Parser/Lexer.hs
--- a/src/Language/PureScript/Parser/Lexer.hs
+++ b/src/Language/PureScript/Parser/Lexer.hs
@@ -70,7 +70,6 @@
 import Control.Monad (void, guard)
 import Control.Monad.Identity (Identity)
 import Data.Char (isSpace, isAscii, isSymbol, isAlphaNum)
-import Data.Monoid ((<>))
 import Data.String (fromString)
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/src/Language/PureScript/Pretty/Common.hs b/src/Language/PureScript/Pretty/Common.hs
--- a/src/Language/PureScript/Pretty/Common.hs
+++ b/src/Language/PureScript/Pretty/Common.hs
@@ -10,7 +10,6 @@
 import Control.Monad.State (StateT, modify, get)
 
 import Data.List (elemIndices, intersperse)
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 import Data.Char (isUpper)
@@ -55,11 +54,12 @@
 -- appropriately and advancing source mappings on the right hand side to account for
 -- the length of the left.
 --
+instance Semigroup StrPos where
+  StrPos (a,b,c) <> StrPos (a',b',c') = StrPos (a `addPos` a', b <> b', c ++ (bumpPos a <$> c'))
+
 instance Monoid StrPos where
   mempty = StrPos (SourcePos 0 0, "", [])
 
-  StrPos (a,b,c) `mappend` StrPos (a',b',c') = StrPos (a `addPos` a', b <> b', c ++ (bumpPos a <$> c'))
-
   mconcat ms =
     let s' = foldMap (\(StrPos(_, s, _)) -> s) ms
         (p, maps) = foldl plus (SourcePos 0 0, []) ms
@@ -88,7 +88,7 @@
       mapping = SMap (T.pack file) startPos zeroPos
       zeroPos = SourcePos 0 0
 
-newtype PlainString = PlainString Text deriving Monoid
+newtype PlainString = PlainString Text deriving (Semigroup, Monoid)
 
 runPlainString :: PlainString -> Text
 runPlainString (PlainString s) = s
diff --git a/src/Language/PureScript/Pretty/Kinds.hs b/src/Language/PureScript/Pretty/Kinds.hs
--- a/src/Language/PureScript/Pretty/Kinds.hs
+++ b/src/Language/PureScript/Pretty/Kinds.hs
@@ -10,7 +10,6 @@
 import Control.Arrow (ArrowPlus(..))
 import Control.PatternArrows as PA
 
-import Data.Monoid ((<>))
 import Data.Maybe (fromMaybe)
 import qualified Data.Text as T
 import Data.Text (Text)
diff --git a/src/Language/PureScript/Pretty/Types.hs b/src/Language/PureScript/Pretty/Types.hs
--- a/src/Language/PureScript/Pretty/Types.hs
+++ b/src/Language/PureScript/Pretty/Types.hs
@@ -14,7 +14,7 @@
   , prettyPrintObjectKey
   ) where
 
-import Prelude.Compat
+import Prelude.Compat hiding ((<>))
 
 import Control.Arrow ((<+>))
 import Control.PatternArrows as PA
diff --git a/src/Language/PureScript/Pretty/Values.hs b/src/Language/PureScript/Pretty/Values.hs
--- a/src/Language/PureScript/Pretty/Values.hs
+++ b/src/Language/PureScript/Pretty/Values.hs
@@ -7,7 +7,7 @@
   , prettyPrintBinderAtom
   ) where
 
-import Prelude.Compat
+import Prelude.Compat hiding ((<>))
 
 import Control.Arrow (second)
 
diff --git a/src/Language/PureScript/Publish.hs b/src/Language/PureScript/Publish.hs
--- a/src/Language/PureScript/Publish.hs
+++ b/src/Language/PureScript/Publish.hs
@@ -36,7 +36,8 @@
 import Data.Time.Clock (UTCTime)
 import Data.Time.Clock.POSIX (posixSecondsToUTCTime)
 import Data.Version
-import qualified Data.SPDX as SPDX
+import qualified Distribution.SPDX as SPDX
+import qualified Distribution.Parsec.Class as CabalParsec
 
 import System.Directory (doesFileExist)
 import System.FilePath.Glob (globDir1)
@@ -230,7 +231,11 @@
 -- Check if a string is a valid SPDX license expression.
 --
 isValidSPDX :: String -> Bool
-isValidSPDX = (== 1) . length . SPDX.parseExpression
+isValidSPDX input = case CabalParsec.simpleParsec input of
+  Nothing -> False
+  Just SPDX.NONE -> False
+  Just _ -> True
+
 
 extractGithub :: Text -> Maybe (D.GithubUser, D.GithubRepo)
 extractGithub = stripGitHubPrefixes
diff --git a/src/Language/PureScript/Publish/ErrorsWarnings.hs b/src/Language/PureScript/Publish/ErrorsWarnings.hs
--- a/src/Language/PureScript/Publish/ErrorsWarnings.hs
+++ b/src/Language/PureScript/Publish/ErrorsWarnings.hs
@@ -311,11 +311,12 @@
   }
   deriving (Show, Eq, Ord)
 
+instance Semigroup CollectedWarnings where
+  (CollectedWarnings as bs cs d es) <> (CollectedWarnings as' bs' cs' d' es') =
+    CollectedWarnings (as <> as') (bs <> bs') (cs <> cs') (d <> d') (es <> es')
+
 instance Monoid CollectedWarnings where
   mempty = CollectedWarnings mempty mempty mempty mempty mempty
-  mappend (CollectedWarnings as bs cs d es)
-          (CollectedWarnings as' bs' cs' d' es') =
-    CollectedWarnings (as <> as') (bs <> bs') (cs <> cs') (d <> d') (es <> es')
 
 collectWarnings :: [PackageWarning] -> CollectedWarnings
 collectWarnings = foldMap singular
diff --git a/src/Language/PureScript/Renamer.hs b/src/Language/PureScript/Renamer.hs
--- a/src/Language/PureScript/Renamer.hs
+++ b/src/Language/PureScript/Renamer.hs
@@ -10,7 +10,6 @@
 import Data.List (find)
 import Data.Maybe (fromJust, fromMaybe)
 import qualified Data.Map as M
-import Data.Monoid ((<>))
 import qualified Data.Set as S
 import qualified Data.Text as T
 
diff --git a/src/Language/PureScript/Sugar/DoNotation.hs b/src/Language/PureScript/Sugar/DoNotation.hs
--- a/src/Language/PureScript/Sugar/DoNotation.hs
+++ b/src/Language/PureScript/Sugar/DoNotation.hs
@@ -25,46 +25,47 @@
 -- | Desugar a single do statement
 desugarDo :: forall m. (MonadSupply m, MonadError MultipleErrors m) => Declaration -> m Declaration
 desugarDo d =
-  let (f, _, _) = everywhereOnValuesM return replace return
-  in rethrowWithPosition (declSourceSpan d) $ f d
+  let ss = declSourceSpan d
+      (f, _, _) = everywhereOnValuesM return (replace ss) return
+  in rethrowWithPosition ss $ f d
   where
-  bind :: Expr
-  bind = Var nullSourceSpan (Qualified Nothing (Ident C.bind))
+  bind :: SourceSpan -> Expr
+  bind = flip Var (Qualified Nothing (Ident C.bind))
 
-  discard :: Expr
-  discard = Var nullSourceSpan (Qualified Nothing (Ident C.discard))
+  discard :: SourceSpan -> Expr
+  discard = flip Var (Qualified Nothing (Ident C.discard))
 
-  replace :: Expr -> m Expr
-  replace (Do els) = go els
-  replace (PositionedValue pos com v) = PositionedValue pos com <$> rethrowWithPosition pos (replace v)
-  replace other = return other
+  replace :: SourceSpan -> Expr -> m Expr
+  replace pos (Do els) = go pos els
+  replace _ (PositionedValue pos com v) = PositionedValue pos com <$> rethrowWithPosition pos (replace pos v)
+  replace _ other = return other
 
-  go :: [DoNotationElement] -> m Expr
-  go [] = internalError "The impossible happened in desugarDo"
-  go [DoNotationValue val] = return val
-  go (DoNotationValue val : rest) = do
-    rest' <- go rest
-    return $ App (App discard val) (Abs (VarBinder nullSourceSpan UnusedIdent) rest')
-  go [DoNotationBind _ _] = throwError . errorMessage $ InvalidDoBind
-  go (DoNotationBind b _ : _) | First (Just ident) <- foldMap fromIdent (binderNames b) =
+  go :: SourceSpan -> [DoNotationElement] -> m Expr
+  go _ [] = internalError "The impossible happened in desugarDo"
+  go _ [DoNotationValue val] = return val
+  go pos (DoNotationValue val : rest) = do
+    rest' <- go pos rest
+    return $ App (App (discard pos) val) (Abs (VarBinder pos UnusedIdent) rest')
+  go _ [DoNotationBind _ _] = throwError . errorMessage $ InvalidDoBind
+  go _ (DoNotationBind b _ : _) | First (Just ident) <- foldMap fromIdent (binderNames b) =
       throwError . errorMessage $ CannotUseBindWithDo (Ident ident)
     where
       fromIdent (Ident i) | i `elem` [ C.bind, C.discard ] = First (Just i)
       fromIdent _ = mempty
-  go (DoNotationBind (VarBinder ss ident) val : rest) = do
-    rest' <- go rest
-    return $ App (App bind val) (Abs (VarBinder ss ident) rest')
-  go (DoNotationBind binder val : rest) = do
-    rest' <- go rest
+  go pos (DoNotationBind (VarBinder ss ident) val : rest) = do
+    rest' <- go pos rest
+    return $ App (App (bind pos) val) (Abs (VarBinder ss ident) rest')
+  go pos (DoNotationBind binder val : rest) = do
+    rest' <- go pos rest
     ident <- freshIdent'
-    return $ App (App bind val) (Abs (VarBinder nullSourceSpan ident) (Case [Var nullSourceSpan (Qualified Nothing ident)] [CaseAlternative [binder] [MkUnguarded rest']]))
-  go [DoNotationLet _] = throwError . errorMessage $ InvalidDoLet
-  go (DoNotationLet ds : rest) = do
+    return $ App (App (bind pos) val) (Abs (VarBinder pos ident) (Case [Var pos (Qualified Nothing ident)] [CaseAlternative [binder] [MkUnguarded rest']]))
+  go _ [DoNotationLet _] = throwError . errorMessage $ InvalidDoLet
+  go pos (DoNotationLet ds : rest) = do
     let checkBind :: Declaration -> m ()
         checkBind (ValueDecl (ss, _) i@(Ident name) _ _ _)
           | name `elem` [ C.bind, C.discard ] = throwError . errorMessage' ss $ CannotUseBindWithDo i
         checkBind _ = pure ()
     mapM_ checkBind ds
-    rest' <- go rest
+    rest' <- go pos rest
     return $ Let FromLet ds rest'
-  go (PositionedDoNotationElement pos com el : rest) = rethrowWithPosition pos $ PositionedValue pos com <$> go (el : rest)
+  go _ (PositionedDoNotationElement pos com el : rest) = rethrowWithPosition pos $ PositionedValue pos com <$> go pos (el : rest)
diff --git a/src/Language/PureScript/Sugar/Names/Env.hs b/src/Language/PureScript/Sugar/Names/Env.hs
--- a/src/Language/PureScript/Sugar/Names/Env.hs
+++ b/src/Language/PureScript/Sugar/Names/Env.hs
@@ -32,6 +32,7 @@
 import Data.Foldable (find)
 import Data.List (groupBy, sortBy, delete)
 import Data.Maybe (fromJust, mapMaybe)
+import Safe (headMay)
 import qualified Data.Map as M
 import qualified Data.Set as S
 
@@ -469,8 +470,9 @@
   in
     if length groups > 1
     then case nonImplicit of
-      [ImportRecord (Qualified (Just mnNew) _) mnOrig ss' _] -> do
+      [ImportRecord (Qualified (Just mnNew) _) mnOrig _ _] -> do
         let warningModule = if mnNew == currentModule then Nothing else Just mnNew
+            ss' = maybe nullSourceSpan importSourceSpan . headMay . filter ((== FromImplicit) . importProvenance) $ xs
         tell . errorMessage' ss' $ ScopeShadowing name warningModule $ delete mnNew conflictModules
         return (mnNew, mnOrig)
       _ -> throwError . errorMessage' ss $ ScopeConflict name conflictModules
diff --git a/src/Language/PureScript/Sugar/Names/Exports.hs b/src/Language/PureScript/Sugar/Names/Exports.hs
--- a/src/Language/PureScript/Sugar/Names/Exports.hs
+++ b/src/Language/PureScript/Sugar/Names/Exports.hs
@@ -147,6 +147,7 @@
     -- values if that fails to see whether the value has been imported at all.
     testQuals :: (forall a b. M.Map (Qualified a) b -> [Qualified a]) -> ModuleName -> Bool
     testQuals f mn' = any (isQualifiedWith mn') (f (importedTypes imps))
+                   || any (isQualifiedWith mn') (f (importedTypeOps imps))
                    || any (isQualifiedWith mn') (f (importedDataConstructors imps))
                    || any (isQualifiedWith mn') (f (importedTypeClasses imps))
                    || any (isQualifiedWith mn') (f (importedValues imps))
diff --git a/src/Language/PureScript/Sugar/TypeClasses.hs b/src/Language/PureScript/Sugar/TypeClasses.hs
--- a/src/Language/PureScript/Sugar/TypeClasses.hs
+++ b/src/Language/PureScript/Sugar/TypeClasses.hs
@@ -14,9 +14,11 @@
 import           Control.Monad.Error.Class (MonadError(..))
 import           Control.Monad.State
 import           Control.Monad.Supply.Class
-import           Data.List ((\\), find, sortBy)
+import           Data.List (find, sortBy)
 import qualified Data.Map as M
 import           Data.Maybe (catMaybes, mapMaybe, isJust, fromMaybe)
+import qualified Data.List.NonEmpty as NEL
+import qualified Data.Set as S
 import           Data.Text (Text)
 import qualified Language.PureScript.Constants as C
 import           Language.PureScript.Crash
@@ -285,12 +287,14 @@
     maybe (throwError . errorMessage' ss . UnknownName $ fmap TyClassName className) return $
       M.lookup (qualify mn className) m
 
-  case map fst typeClassMembers \\ mapMaybe declIdent decls of
-    member : _ -> throwError . errorMessage' ss $ MissingClassMember member
-    [] -> do
-      -- Replace the type arguments with the appropriate types in the member types
-      let memberTypes = map (second (replaceAllTypeVars (zip (map fst typeClassArguments) tys))) typeClassMembers
+  -- Replace the type arguments with the appropriate types in the member types
+  let memberTypes = map (second (replaceAllTypeVars (zip (map fst typeClassArguments) tys))) typeClassMembers
 
+  let declaredMembers = S.fromList $ mapMaybe declIdent decls
+
+  case filter (\(ident, _) -> not $ S.member ident declaredMembers) memberTypes of
+    hd : tl -> throwError . errorMessage' ss $ MissingClassMember (hd NEL.:| tl)
+    [] -> do
       -- Create values for the type instance members
       members <- zip (map typeClassMemberName decls) <$> traverse (memberToValue memberTypes) decls
 
diff --git a/src/Language/PureScript/Sugar/TypeClasses/Deriving.hs b/src/Language/PureScript/Sugar/TypeClasses/Deriving.hs
--- a/src/Language/PureScript/Sugar/TypeClasses/Deriving.hs
+++ b/src/Language/PureScript/Sugar/TypeClasses/Deriving.hs
@@ -12,7 +12,6 @@
 import           Data.Foldable (for_)
 import           Data.List (foldl', find, sortBy, unzip5)
 import qualified Data.Map as M
-import           Data.Monoid ((<>))
 import           Data.Maybe (fromMaybe, mapMaybe)
 import           Data.Ord (comparing)
 import qualified Data.Set as S
@@ -42,13 +41,15 @@
   -- ^ A list of newtype instances which were derived in this module.
   } deriving Show
 
-instance Monoid NewtypeDerivedInstances where
-  mempty = NewtypeDerivedInstances mempty mempty
-  mappend x y =
+instance Semigroup NewtypeDerivedInstances where
+  x <> y =
     NewtypeDerivedInstances { ndiClasses          = ndiClasses          x <> ndiClasses          y
                             , ndiDerivedInstances = ndiDerivedInstances x <> ndiDerivedInstances y
                             }
 
+instance Monoid NewtypeDerivedInstances where
+  mempty = NewtypeDerivedInstances mempty mempty
+
 -- | Extract the name of the newtype appearing in the last type argument of
 -- a derived newtype instance.
 --
@@ -201,7 +202,7 @@
   -> m Expr
 deriveNewtypeInstance ss mn syns ndis className ds tys tyConNm dargs = do
     verifySuperclasses
-    tyCon <- findTypeDecl tyConNm ds
+    tyCon <- findTypeDecl ss tyConNm ds
     go tyCon
   where
     go (DataDeclaration _ Newtype _ tyArgNames [(_, [wrapped])]) = do
@@ -287,7 +288,7 @@
   -> m ([Declaration], Type)
 deriveGenericRep ss mn syns ds tyConNm tyConArgs repTy = do
     checkIsWildcard ss tyConNm repTy
-    go =<< findTypeDecl tyConNm ds
+    go =<< findTypeDecl ss tyConNm ds
   where
     go :: Declaration -> m ([Declaration], Type)
     go (DataDeclaration (ss', _) _ _ args dctors) = do
@@ -440,7 +441,7 @@
   -> ProperName 'TypeName
   -> m [Declaration]
 deriveEq ss mn syns ds tyConNm = do
-  tyCon <- findTypeDecl tyConNm ds
+  tyCon <- findTypeDecl ss tyConNm ds
   eqFun <- mkEqFunction tyCon
   return [ ValueDecl (ss, []) (Ident C.eq) Public [] (unguarded eqFun) ]
   where
@@ -508,7 +509,7 @@
   -> ProperName 'TypeName
   -> m [Declaration]
 deriveOrd ss mn syns ds tyConNm = do
-  tyCon <- findTypeDecl tyConNm ds
+  tyCon <- findTypeDecl ss tyConNm ds
   compareFun <- mkCompareFunction tyCon
   return [ ValueDecl (ss, []) (Ident C.compare) Public [] (unguarded compareFun) ]
   where
@@ -612,7 +613,7 @@
   -> m ([Declaration], Type)
 deriveNewtype ss mn syns ds tyConNm tyConArgs unwrappedTy = do
     checkIsWildcard ss tyConNm unwrappedTy
-    go =<< findTypeDecl tyConNm ds
+    go =<< findTypeDecl ss tyConNm ds
   where
     go :: Declaration -> m ([Declaration], Type)
     go (DataDeclaration (ss', _) Data name _ _) =
@@ -639,10 +640,11 @@
 
 findTypeDecl
   :: (MonadError MultipleErrors m)
-  => ProperName 'TypeName
+  => SourceSpan
+  -> ProperName 'TypeName
   -> [Declaration]
   -> m Declaration
-findTypeDecl tyConNm = maybe (throwError . errorMessage $ CannotFindDerivingType tyConNm) return . find isTypeDecl
+findTypeDecl ss tyConNm = maybe (throwError . errorMessage' ss $ CannotFindDerivingType tyConNm) return . find isTypeDecl
   where
   isTypeDecl :: Declaration -> Bool
   isTypeDecl (DataDeclaration _ _ nm _ _) | nm == tyConNm = True
@@ -692,7 +694,7 @@
   -> ProperName 'TypeName
   -> m [Declaration]
 deriveFunctor ss mn syns ds tyConNm = do
-  tyCon <- findTypeDecl tyConNm ds
+  tyCon <- findTypeDecl ss tyConNm ds
   mapFun <- mkMapFunction tyCon
   return [ ValueDecl (ss, []) (Ident C.map) Public [] (unguarded mapFun) ]
   where
diff --git a/src/Language/PureScript/TypeChecker.hs b/src/Language/PureScript/TypeChecker.hs
--- a/src/Language/PureScript/TypeChecker.hs
+++ b/src/Language/PureScript/TypeChecker.hs
@@ -17,12 +17,10 @@
 import Control.Monad.State.Class (MonadState(..), modify, gets)
 import Control.Monad.Supply.Class (MonadSupply)
 import Control.Monad.Writer.Class (MonadWriter(..))
-import Control.Lens ((^..), _1, _2)
 
 import Data.Foldable (for_, traverse_, toList)
 import Data.List (nub, nubBy, (\\), sort, group)
 import Data.Maybe
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.List.NonEmpty as NEL
 import qualified Data.Map as M
@@ -42,6 +40,8 @@
 import Language.PureScript.TypeChecker.Types as T
 import Language.PureScript.TypeClassDictionaries
 import Language.PureScript.Types
+
+import Lens.Micro.Platform ((^..), _1, _2)
 
 addDataType
   :: (MonadState CheckState m, MonadError MultipleErrors m, MonadWriter MultipleErrors m)
diff --git a/src/Language/PureScript/TypeChecker/Entailment.hs b/src/Language/PureScript/TypeChecker/Entailment.hs
--- a/src/Language/PureScript/TypeChecker/Entailment.hs
+++ b/src/Language/PureScript/TypeChecker/Entailment.hs
@@ -135,13 +135,14 @@
   | Unknown
   deriving (Eq, Show, Functor)
 
+instance Semigroup t => Semigroup (Matched t) where
+  (Match l) <> (Match r) = Match (l <> r)
+  Apart     <> _         = Apart
+  _         <> Apart     = Apart
+  _         <> _         = Unknown
+
 instance Monoid t => Monoid (Matched t) where
   mempty = Match mempty
-
-  mappend (Match l) (Match r) = Match (l <> r)
-  mappend Apart     _         = Apart
-  mappend _         Apart     = Apart
-  mappend _         _         = Unknown
 
 -- | Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
 -- return a type class dictionary reference.
diff --git a/src/Language/PureScript/TypeChecker/Skolems.hs b/src/Language/PureScript/TypeChecker/Skolems.hs
--- a/src/Language/PureScript/TypeChecker/Skolems.hs
+++ b/src/Language/PureScript/TypeChecker/Skolems.hs
@@ -14,7 +14,6 @@
 import Control.Monad.State.Class (MonadState(..), gets, modify)
 import Data.Foldable (traverse_)
 import Data.Functor.Identity (Identity(), runIdentity)
-import Data.Monoid
 import Data.Set (Set, fromList, notMember)
 import Data.Text (Text)
 import Language.PureScript.AST
diff --git a/src/Language/PureScript/TypeChecker/Types.hs b/src/Language/PureScript/TypeChecker/Types.hs
--- a/src/Language/PureScript/TypeChecker/Types.hs
+++ b/src/Language/PureScript/TypeChecker/Types.hs
@@ -39,7 +39,6 @@
 import Data.Functor (($>))
 import Data.List (transpose, (\\), partition, delete)
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import Data.Traversable (for)
 import qualified Data.List.NonEmpty as NEL
 import qualified Data.Map as M
diff --git a/src/Language/PureScript/TypeClassDictionaries.hs b/src/Language/PureScript/TypeClassDictionaries.hs
--- a/src/Language/PureScript/TypeClassDictionaries.hs
+++ b/src/Language/PureScript/TypeClassDictionaries.hs
@@ -7,7 +7,6 @@
 
 import GHC.Generics (Generic)
 import Control.DeepSeq (NFData)
-import Data.Monoid ((<>))
 import Data.Text (Text, pack)
 
 import Language.PureScript.Names
diff --git a/src/Language/PureScript/Types.hs b/src/Language/PureScript/Types.hs
--- a/src/Language/PureScript/Types.hs
+++ b/src/Language/PureScript/Types.hs
@@ -18,7 +18,6 @@
 import Data.List (sortBy)
 import Data.Ord (comparing)
 import Data.Maybe (fromMaybe)
-import Data.Monoid ((<>))
 import Data.Text (Text)
 import qualified Data.Text as T
 import GHC.Generics (Generic)
diff --git a/stack.yaml b/stack.yaml
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,8 @@
-resolver: lts-11.7
+resolver: lts-12.0
 packages:
 - '.'
 extra-deps:
+nix:
+  enable: false
+  packages:
+  - zlib
diff --git a/tests/Language/PureScript/Ide/CompletionSpec.hs b/tests/Language/PureScript/Ide/CompletionSpec.hs
--- a/tests/Language/PureScript/Ide/CompletionSpec.hs
+++ b/tests/Language/PureScript/Ide/CompletionSpec.hs
@@ -4,7 +4,8 @@
 
 import Protolude
 
-import Language.PureScript as P
+import qualified Data.Set as Set
+import qualified Language.PureScript as P
 import Language.PureScript.Ide.Test as Test
 import Language.PureScript.Ide.Command as Command
 import Language.PureScript.Ide.Completion
@@ -30,7 +31,7 @@
 load = LoadSync . map Test.mn
 
 rebuildSync :: FilePath -> Command
-rebuildSync fp = RebuildSync ("src" </> fp) Nothing
+rebuildSync fp = RebuildSync ("src" </> fp) Nothing (Set.singleton P.JS)
 
 spec :: Spec
 spec = describe "Applying completion options" $ do
diff --git a/tests/Language/PureScript/Ide/RebuildSpec.hs b/tests/Language/PureScript/Ide/RebuildSpec.hs
--- a/tests/Language/PureScript/Ide/RebuildSpec.hs
+++ b/tests/Language/PureScript/Ide/RebuildSpec.hs
@@ -4,6 +4,8 @@
 
 import           Protolude
 
+import qualified Data.Set as Set
+import qualified Language.PureScript as P
 import           Language.PureScript.AST.SourcePos (spanName)
 import           Language.PureScript.Ide.Command
 import           Language.PureScript.Ide.Completion
@@ -11,16 +13,20 @@
 import           Language.PureScript.Ide.Types
 import qualified Language.PureScript.Ide.Test as Test
 import           System.FilePath
+import           System.Directory (doesFileExist, removePathForcibly)
 import           Test.Hspec
 
+defaultTarget :: Set P.CodegenTarget
+defaultTarget = Set.singleton P.JS
+
 load :: [Text] -> Command
 load = LoadSync . map Test.mn
 
 rebuild :: FilePath -> Command
-rebuild fp = Rebuild ("src" </> fp) Nothing
+rebuild fp = Rebuild ("src" </> fp) Nothing defaultTarget
 
 rebuildSync :: FilePath -> Command
-rebuildSync fp = RebuildSync ("src" </> fp) Nothing
+rebuildSync fp = RebuildSync ("src" </> fp) Nothing defaultTarget
 
 spec :: Spec
 spec = describe "Rebuilding single modules" $ do
@@ -67,6 +73,20 @@
         Test.runIde'
           editorConfig
           emptyIdeState
-          [ RebuildSync ("src" </> "RebuildSpecWithHiddenIdent.purs") (Just "actualFile")
+          [ RebuildSync ("src" </> "RebuildSpecWithHiddenIdent.purs") (Just "actualFile") defaultTarget
           , Complete [] (flexMatcher "hid") (Just (Test.mn "RebuildSpecWithHiddenIdent")) defaultCompletionOptions]
       map spanName (complLocation result) `shouldBe` Just "actualFile"
+    it "doesn't produce JS when an empty target list is supplied" $ do
+      exists <- Test.inProject $ do
+        let indexJs = "output" </> "RebuildSpecSingleModule" </> "index.js"
+        removePathForcibly ("output" </> "RebuildSpecSingleModule")
+        _ <- Test.runIde [ RebuildSync ("src" </> "RebuildSpecSingleModule.purs") Nothing Set.empty ]
+        doesFileExist indexJs
+      exists `shouldBe` False
+    it "does produce corefn if it's a codegen target" $ do
+      exists <- Test.inProject $ do
+        let corefn = "output" </> "RebuildSpecSingleModule" </> "corefn.json"
+        removePathForcibly ("output" </> "RebuildSpecSingleModule")
+        _ <- Test.runIde [ RebuildSync ("src" </> "RebuildSpecSingleModule.purs") Nothing (Set.singleton P.CoreFn) ]
+        doesFileExist corefn
+      exists `shouldBe` True
diff --git a/tests/Language/PureScript/Ide/StateSpec.hs b/tests/Language/PureScript/Ide/StateSpec.hs
--- a/tests/Language/PureScript/Ide/StateSpec.hs
+++ b/tests/Language/PureScript/Ide/StateSpec.hs
@@ -3,11 +3,11 @@
 module Language.PureScript.Ide.StateSpec where
 
 import           Protolude
-import           Control.Lens hiding ((&))
 import           Language.PureScript.Ide.Types
 import           Language.PureScript.Ide.State
 import           Language.PureScript.Ide.Test
 import qualified Language.PureScript as P
+import           Lens.Micro.Platform hiding ((&))
 import           Test.Hspec
 import qualified Data.Map as Map
 
@@ -91,7 +91,7 @@
     it "resolves an instance for an existing type class" $ do
       resolveInstances (Map.singleton (mn "InstanceModule") ef) moduleMap
         `shouldSatisfy`
-        elemOf (ix (mn "ClassModule") . ix 0 . idaDeclaration . _IdeDeclTypeClass . ideTCInstances . folded) ideInstance
+        anyOf (ix (mn "ClassModule") . ix 0 . idaDeclaration . _IdeDeclTypeClass . ideTCInstances . folded) (ideInstance ==)
   describe "resolving data constructors" $ do
     it "resolves a constructor" $ do
       resolveDataConstructorsForModule (snd testModule)
diff --git a/tests/TestCompiler.hs b/tests/TestCompiler.hs
--- a/tests/TestCompiler.hs
+++ b/tests/TestCompiler.hs
@@ -40,7 +40,6 @@
 import Control.Arrow ((***), (>>>))
 
 import Control.Monad.Reader
-import Control.Monad.Writer.Strict
 import Control.Monad.Trans.Except
 
 import System.Exit
@@ -234,13 +233,25 @@
 
 checkPositioned :: P.MultipleErrors -> Maybe String
 checkPositioned errs =
-  case mapMaybe (\err -> maybe (Just err) (const Nothing) (P.errorSpan err)) (P.runMultipleErrors errs) of
+  case mapMaybe guardSpans (P.runMultipleErrors errs) of
     [] ->
       Nothing
     errs' ->
       Just
         $ "Found errors with missing source spans:\n"
         ++ unlines (map (P.renderBox . P.prettyPrintSingleError P.defaultPPEOptions) errs')
+  where
+  guardSpans :: P.ErrorMessage -> Maybe P.ErrorMessage
+  guardSpans err = case P.errorSpan err of
+    Just ss | any (not . isNonsenseSpan) ss -> Nothing
+    _ -> Just err
+
+  isNonsenseSpan :: P.SourceSpan -> Bool
+  isNonsenseSpan (P.SourceSpan spanName spanStart spanEnd) =
+    spanName == "" || spanName == "<module>" || (spanStart == emptyPos && spanEnd == emptyPos)
+
+  emptyPos :: P.SourcePos
+  emptyPos = P.SourcePos 0 0
 
 assertCompiles
   :: [P.Module]
diff --git a/tests/TestCoreFn.hs b/tests/TestCoreFn.hs
--- a/tests/TestCoreFn.hs
+++ b/tests/TestCoreFn.hs
@@ -9,7 +9,7 @@
 import Prelude.Compat
 
 import Data.Aeson
-import Data.Aeson.Types
+import Data.Aeson.Types as Aeson
 import Data.Version
 
 import Language.PureScript.AST.Literals
@@ -37,7 +37,7 @@
   in snd <$> parseModule (moduleToJSON v m)
 
 isSuccess :: Result a -> Bool
-isSuccess (Success _) = True
+isSuccess (Aeson.Success _) = True
 isSuccess _           = False
 
 spec :: Spec
@@ -52,42 +52,42 @@
     r `shouldSatisfy` isSuccess
     case r of
       Error _   -> return ()
-      Success m -> moduleName m `shouldBe` mn
+      Aeson.Success m -> moduleName m `shouldBe` mn
 
   specify "should parse source span" $ do
     let r = parseMod $ Module ss [] mn mp [] [] [] []
     r `shouldSatisfy` isSuccess
     case r of
       Error _   -> return ()
-      Success m -> moduleSourceSpan m `shouldBe` ss
+      Aeson.Success m -> moduleSourceSpan m `shouldBe` ss
 
   specify "should parse module path" $ do
     let r = parseMod $ Module ss [] mn mp [] [] [] []
     r `shouldSatisfy` isSuccess
     case r of
       Error _   -> return ()
-      Success m -> modulePath m `shouldBe` mp
+      Aeson.Success m -> modulePath m `shouldBe` mp
 
   specify "should parse imports" $ do
     let r = parseMod $ Module ss [] mn mp [(ann, mn)] [] [] []
     r `shouldSatisfy` isSuccess
     case r of
       Error _   -> return ()
-      Success m -> moduleImports m `shouldBe` [(ann, mn)]
+      Aeson.Success m -> moduleImports m `shouldBe` [(ann, mn)]
 
   specify "should parse exports" $ do
     let r = parseMod $ Module ss [] mn mp [] [Ident "exp"] [] []
     r `shouldSatisfy` isSuccess
     case r of
       Error _   -> return ()
-      Success m -> moduleExports m `shouldBe` [Ident "exp"]
+      Aeson.Success m -> moduleExports m `shouldBe` [Ident "exp"]
 
   specify "should parse foreign" $ do
     let r = parseMod $ Module ss [] mn mp [] [] [Ident "exp"] []
     r `shouldSatisfy` isSuccess
     case r of
       Error _   -> return ()
-      Success m -> moduleForeign m `shouldBe` [Ident "exp"]
+      Aeson.Success m -> moduleForeign m `shouldBe` [Ident "exp"]
 
   context "Expr" $ do
     specify "should parse literals" $ do
diff --git a/tests/TestPrimDocs.hs b/tests/TestPrimDocs.hs
--- a/tests/TestPrimDocs.hs
+++ b/tests/TestPrimDocs.hs
@@ -3,7 +3,6 @@
 import Prelude
 
 import Control.Monad
-import Data.Monoid ((<>))
 import Data.List ((\\))
 import qualified Data.Map as Map
 import qualified Data.Set as Set
diff --git a/tests/TestPsci/CommandTest.hs b/tests/TestPsci/CommandTest.hs
--- a/tests/TestPsci/CommandTest.hs
+++ b/tests/TestPsci/CommandTest.hs
@@ -1,10 +1,16 @@
+{-# LANGUAGE OverloadedStrings #-}
+
 module TestPsci.CommandTest where
 
 import Prelude ()
 import Prelude.Compat
 
+import Control.Monad.IO.Class (liftIO)
 import Control.Monad.Trans.RWS.Strict (get)
+import Language.PureScript (moduleNameFromString)
 import Language.PureScript.Interactive
+import System.FilePath ((</>))
+import System.Directory (getCurrentDirectory)
 import Test.Hspec
 import TestPsci.TestEnv
 
@@ -42,5 +48,20 @@
     ":complete M.a" `prints` unlines ["M.ap", "M.apply"]
 
   specPSCi ":browse" $ do
+    ":browse Data.Void" `printed` flip shouldContain "data Void"
+    ":browse Data.Void" `printed` flip shouldContain "absurd ::"
+
+  specPSCi ":reload, :browse" $ do
+    cwd <- liftIO getCurrentDirectory
+    let new = cwd </> "tests" </> "support" </> "psci" </> "Reload.edit"
+
+    ":browse Reload" `printed` flip shouldContain    "reload ::"
+    ":browse Reload" `printed` flip shouldNotContain "edited ::"
+
+    simulateModuleEdit (moduleNameFromString "Reload") new $ do
+      run ":reload"
+      ":browse Reload" `printed` flip shouldNotContain "reload ::"
+      ":browse Reload" `printed` flip shouldContain    "edited ::"
+
     ":browse Mirp" `printed` flip shouldContain "is not valid"
     ":browse Prim" `printed` flip shouldContain "class Partial"
diff --git a/tests/TestPsci/CompletionTest.hs b/tests/TestPsci/CompletionTest.hs
--- a/tests/TestPsci/CompletionTest.hs
+++ b/tests/TestPsci/CompletionTest.hs
@@ -34,12 +34,12 @@
   , (":b",  [":browse"])
 
   -- :browse should complete module names
-  , (":b Eff",    map (":b Effect" ++) ["", ".Unsafe", ".Class", ".Console", ".Uncurried", ".Ref"])
-  , (":b Effect.", map (":b Effect" ++) [".Unsafe", ".Class", ".Console", ".Uncurried", ".Ref"])
+  , (":b Eff",    map (":b Effect" ++) ["", ".Unsafe", ".Class", ".Class.Console", ".Console", ".Uncurried", ".Ref"])
+  , (":b Effect.", map (":b Effect" ++) [".Unsafe", ".Class", ".Class.Console", ".Console", ".Uncurried", ".Ref"])
 
   -- import should complete module names
-  , ("import Eff",    map ("import Effect" ++) ["", ".Unsafe", ".Class", ".Console", ".Uncurried", ".Ref"])
-  , ("import Effect.", map ("import Effect" ++) [".Unsafe", ".Class", ".Console", ".Uncurried", ".Ref"])
+  , ("import Eff",    map ("import Effect" ++) ["", ".Unsafe", ".Class", ".Class.Console", ".Console", ".Uncurried", ".Ref"])
+  , ("import Effect.", map ("import Effect" ++) [".Unsafe", ".Class", ".Class.Console", ".Console", ".Uncurried", ".Ref"])
 
   -- :quit, :help, :reload, :clear should not complete
   , (":help ", [])
diff --git a/tests/TestPsci/TestEnv.hs b/tests/TestPsci/TestEnv.hs
--- a/tests/TestPsci/TestEnv.hs
+++ b/tests/TestPsci/TestEnv.hs
@@ -1,16 +1,21 @@
+{-# LANGUAGE OverloadedStrings #-}
+
 module TestPsci.TestEnv where
 
 import Prelude ()
 import Prelude.Compat
 
-import           Control.Monad (void)
+import           Control.Exception.Lifted (bracket_)
+import           Control.Monad (void, when)
 import           Control.Monad.IO.Class (liftIO)
-import           Control.Monad.Trans.RWS.Strict (evalRWST, RWST)
+import           Control.Monad.Trans.RWS.Strict (evalRWST, asks, local, RWST)
+import           Data.List (isSuffixOf)
+import qualified Data.Text as T
 import qualified Language.PureScript as P
 import           Language.PureScript.Interactive
-import           System.Directory (getCurrentDirectory)
+import           System.Directory (getCurrentDirectory, doesPathExist, removeFile)
 import           System.Exit
-import           System.FilePath ((</>))
+import           System.FilePath ((</>), pathSeparator)
 import qualified System.FilePath.Glob as Glob
 import           System.Process (readProcessWithExitCode)
 import           Test.Hspec (shouldBe, Expectation)
@@ -23,9 +28,10 @@
 initTestPSCiEnv = do
   -- Load test support packages
   cwd <- getCurrentDirectory
-  let supportDir = cwd </> "tests" </> "support" </> "bower_components"
-  let supportFiles ext = Glob.globDir1 (Glob.compile ("purescript-*/src/**/*." ++ ext)) supportDir
-  pursFiles <- supportFiles "purs"
+  let supportDir = cwd </> "tests" </> "support"
+  psciFiles <- Glob.globDir1 (Glob.compile "**/*.purs") (supportDir </> "psci")
+  libraries <- Glob.globDir1 (Glob.compile "purescript-*/src/**/*.purs") (supportDir </> "bower_components")
+  let pursFiles = psciFiles ++ libraries
   modulesOrError <- loadAllModules pursFiles
   case modulesOrError of
     Left err ->
@@ -35,8 +41,8 @@
       makeResultOrError <- runMake . make $ modules
       case makeResultOrError of
         Left errs -> putStrLn (P.prettyPrintMultipleErrors P.defaultPPEOptions errs) >> exitFailure
-        Right (externs, env) ->
-          return (updateLoadedExterns (const (zip (map snd modules) externs)) initialPSCiState, PSCiConfig pursFiles env)
+        Right (externs, _) ->
+          return (updateLoadedExterns (const (zip (map snd modules) externs)) initialPSCiState, PSCiConfig pursFiles)
 
 -- | Execute a TestPSCi, returning IO
 execTestPSCi :: TestPSCi a -> IO a
@@ -71,9 +77,8 @@
 
 -- | Run a PSCi command, evaluate compiled JS, and ignore evaluation output and printed output
 run :: String -> TestPSCi ()
-run comm = runAndEval comm evalJsAndIgnore ignorePrinted
+run comm = runAndEval comm (void jsEval) ignorePrinted
   where
-    evalJsAndIgnore = jsEval *> return ()
     ignorePrinted _ = return ()
 
 -- | A lifted evaluation of Hspec 'shouldBe' for the TestPSCi
@@ -95,3 +100,29 @@
 
 printed :: String -> (String -> Expectation) -> TestPSCi ()
 printed command f = runAndEval command (void jsEval) (liftIO . f)
+
+simulateModuleEdit :: P.ModuleName -> FilePath -> TestPSCi a -> TestPSCi a
+simulateModuleEdit mn newPath action = do
+  ms <- asks psciFileGlobs
+  case replacePath ms of
+    Nothing  -> fail $ "Did not find " ++ inputPath ++ " in psciFileGlobs"
+    Just xs' -> local (\c -> c { psciFileGlobs = xs' }) temporarily <* rebuild
+
+  where
+  outputPath = modulesDir </> T.unpack (P.runModuleName mn) </> "index.js"
+  inputPath  = T.unpack (T.replace "." slash (P.runModuleName mn)) ++ ".purs"
+  slash      = T.singleton pathSeparator
+
+  replacePath :: [String] -> Maybe [String]
+  replacePath (x:xs)
+    | inputPath `isSuffixOf` x = Just (newPath : xs)
+    | otherwise                = fmap (x:) (replacePath xs)
+  replacePath []               = Nothing
+
+  -- Simply adding the file to `PSCiConfig.fileGlobs` isn't sufficient; running
+  -- ":reload" might not rebuild because the compiled JS artifact has a more
+  -- recent timestamp than the "new" source file `newPath`.
+  temporarily   = bracket_ enableRebuild enableRebuild action
+  enableRebuild = liftIO $ do { b <- doesPathExist outputPath; when b (removeFile outputPath) }
+  rebuild       = handleCommand discard (return ()) discard ReloadState
+  discard _     = return ()
diff --git a/tests/TestUtils.hs b/tests/TestUtils.hs
--- a/tests/TestUtils.hs
+++ b/tests/TestUtils.hs
@@ -66,10 +66,12 @@
 getSupportModuleTuples :: IO [(FilePath, P.Module)]
 getSupportModuleTuples = do
   cd <- getCurrentDirectory
-  let supportDir = cd </> "tests" </> "support" </> "bower_components"
-  supportPurs <- Glob.globDir1 (Glob.compile "purescript-*/src/**/*.purs") supportDir
-  supportPursFiles <- readInput supportPurs
-  modules <- runExceptT $ ExceptT . return $ P.parseModulesFromFiles id supportPursFiles
+  let supportDir = cd </> "tests" </> "support"
+  psciFiles <- Glob.globDir1 (Glob.compile "**/*.purs") (supportDir </> "psci")
+  libraries <- Glob.globDir1 (Glob.compile "purescript-*/src/**/*.purs") (supportDir </> "bower_components")
+  let pursFiles = psciFiles ++ libraries
+  fileContents <- readInput pursFiles
+  modules <- runExceptT $ ExceptT . return $ P.parseModulesFromFiles id fileContents
   case modules of
     Right ms -> return ms
     Left errs -> fail (P.prettyPrintMultipleErrors P.defaultPPEOptions errs)
diff --git a/tests/purs/failing/3405.purs b/tests/purs/failing/3405.purs
new file mode 100644
--- /dev/null
+++ b/tests/purs/failing/3405.purs
@@ -0,0 +1,8 @@
+-- @shouldFailWith CannotFindDerivingType
+module Main where
+
+import Prelude
+
+type Something = Int
+
+derive instance eqSomething ∷ Eq Something
diff --git a/tests/purs/failing/MissingClassMember.purs b/tests/purs/failing/MissingClassMember.purs
--- a/tests/purs/failing/MissingClassMember.purs
+++ b/tests/purs/failing/MissingClassMember.purs
@@ -1,11 +1,10 @@
 -- @shouldFailWith MissingClassMember
 module Main where
 
-import Prelude
-
 class A a where
   a :: a -> String
   b :: a -> Number
+  c :: forall f. a -> f a
 
 instance aString :: A String where
   a s = s
diff --git a/tests/purs/passing/3388.purs b/tests/purs/passing/3388.purs
new file mode 100644
--- /dev/null
+++ b/tests/purs/passing/3388.purs
@@ -0,0 +1,10 @@
+module Main where
+
+import Prelude
+import Effect.Console (log)
+
+main = do
+  let
+    x = { a: 42, b: "foo" }
+    { a, b } = x { a = 43 }
+  log "Done"
diff --git a/tests/purs/passing/3410.purs b/tests/purs/passing/3410.purs
new file mode 100644
--- /dev/null
+++ b/tests/purs/passing/3410.purs
@@ -0,0 +1,11 @@
+module Main
+  ( module Prelude
+  , module DEN
+  , main
+  ) where
+
+import Prelude
+import Data.Either.Nested (type (\/)) as DEN
+import Effect.Console (log)
+
+main = log "Done"
diff --git a/tests/purs/warning/CustomWarning4.purs b/tests/purs/warning/CustomWarning4.purs
new file mode 100644
--- /dev/null
+++ b/tests/purs/warning/CustomWarning4.purs
@@ -0,0 +1,31 @@
+-- @shouldWarnWith UserDefinedWarning
+-- @shouldWarnWith UserDefinedWarning
+-- @shouldWarnWith UserDefinedWarning
+-- @shouldWarnWith UserDefinedWarning
+module Main where
+
+import Prim.TypeError (class Warn, Beside, QuoteLabel, Text)
+import Prim
+import Type.Row (class RowToList, Cons, Nil)
+
+data Label (l :: Symbol) = Label
+
+baz ::
+  forall row label typ.
+  RowToList row (Cons label typ Nil) =>
+  Warn (Beside (Text "Custom label ") (QuoteLabel label)) =>
+  Record row ->
+  String
+baz _ = ""
+
+baz' :: String
+baz' = baz { hello: 1 }
+
+baz'' :: String
+baz'' = baz { "hello": 1 }
+
+baz''' :: String
+baz''' = baz { "h e l l o": 1 }
+
+baz'''' :: String
+baz'''' = baz { "hel\"lo": 1 }
diff --git a/tests/support/bower.json b/tests/support/bower.json
--- a/tests/support/bower.json
+++ b/tests/support/bower.json
@@ -1,77 +1,40 @@
 {
   "name": "purescript-test-suite-support",
   "dependencies": {
-    "purescript-arrays": "purescript/purescript-arrays#compiler/0.12",
-    "purescript-assert": "purescript/purescript-assert#compiler/0.12",
-    "purescript-bifunctors": "purescript/purescript-bifunctors#compiler/0.12",
-    "purescript-console": "purescript/purescript-console#compiler/0.12",
-    "purescript-control": "purescript/purescript-control#compiler/0.12",
-    "purescript-distributive": "purescript/purescript-distributive#compiler/0.12",
-    "purescript-effect": "purescript/purescript-effect#compiler/0.12",
-    "purescript-either": "purescript/purescript-either#compiler/0.12",
-    "purescript-foldable-traversable": "purescript/purescript-foldable-traversable#compiler/0.12",
-    "purescript-functions": "purescript/purescript-functions#compiler/0.12",
-    "purescript-gen": "purescript/purescript-gen#compiler/0.12",
-    "purescript-generics-rep": "purescript/purescript-generics-rep#compiler/0.12",
-    "purescript-globals": "purescript/purescript-globals#compiler/0.12",
-    "purescript-identity": "purescript/purescript-identity#compiler/0.12",
-    "purescript-integers": "purescript/purescript-integers#compiler/0.12",
-    "purescript-invariant": "purescript/purescript-invariant#compiler/0.12",
-    "purescript-lazy": "purescript/purescript-lazy#compiler/0.12",
-    "purescript-lists": "purescript/purescript-lists#compiler/0.12",
-    "purescript-math": "purescript/purescript-math#compiler/0.12",
-    "purescript-maybe": "purescript/purescript-maybe#compiler/0.12",
-    "purescript-newtype": "purescript/purescript-newtype#compiler/0.12",
-    "purescript-nonempty": "purescript/purescript-nonempty#compiler/0.12",
-    "purescript-partial": "purescript/purescript-partial#compiler/0.12",
-    "purescript-prelude": "purescript/purescript-prelude#compiler/0.12",
-    "purescript-proxy": "purescript/purescript-proxy#compiler/0.12",
-    "purescript-psci-support": "purescript/purescript-psci-support#compiler/0.12",
-    "purescript-refs": "purescript/purescript-refs#compiler/0.12",
-    "purescript-st": "purescript/purescript-st#compiler/0.12",
-    "purescript-strings": "purescript/purescript-strings#compiler/0.12",
-    "purescript-tailrec": "purescript/purescript-tailrec#compiler/0.12",
-    "purescript-tuples": "purescript/purescript-tuples#compiler/0.12",
-    "purescript-type-equality": "purescript/purescript-type-equality#compiler/0.12",
-    "purescript-typelevel-prelude": "purescript/purescript-typelevel-prelude#compiler/0.12",
-    "purescript-unfoldable": "purescript/purescript-unfoldable#compiler/0.12",
-    "purescript-unsafe-coerce": "purescript/purescript-unsafe-coerce#compiler/0.12"
-  },
-  "resolutions": {
-    "purescript-arrays": "compiler/0.12",
-    "purescript-assert": "compiler/0.12",
-    "purescript-bifunctors": "compiler/0.12",
-    "purescript-console": "compiler/0.12",
-    "purescript-control": "compiler/0.12",
-    "purescript-distributive": "compiler/0.12",
-    "purescript-effect": "compiler/0.12",
-    "purescript-either": "compiler/0.12",
-    "purescript-foldable-traversable": "compiler/0.12",
-    "purescript-functions": "compiler/0.12",
-    "purescript-gen": "compiler/0.12",
-    "purescript-generics-rep": "compiler/0.12",
-    "purescript-globals": "compiler/0.12",
-    "purescript-identity": "compiler/0.12",
-    "purescript-integers": "compiler/0.12",
-    "purescript-invariant": "compiler/0.12",
-    "purescript-lazy": "compiler/0.12",
-    "purescript-lists": "compiler/0.12",
-    "purescript-math": "compiler/0.12",
-    "purescript-maybe": "compiler/0.12",
-    "purescript-newtype": "compiler/0.12",
-    "purescript-nonempty": "compiler/0.12",
-    "purescript-partial": "compiler/0.12",
-    "purescript-prelude": "compiler/0.12",
-    "purescript-proxy": "compiler/0.12",
-    "purescript-psci-support": "compiler/0.12",
-    "purescript-refs": "compiler/0.12",
-    "purescript-st": "compiler/0.12",
-    "purescript-strings": "compiler/0.12",
-    "purescript-tailrec": "compiler/0.12",
-    "purescript-tuples": "compiler/0.12",
-    "purescript-type-equality": "compiler/0.12",
-    "purescript-typelevel-prelude": "compiler/0.12",
-    "purescript-unfoldable": "compiler/0.12",
-    "purescript-unsafe-coerce": "compiler/0.12"
+    "purescript-arrays": "5.0.0",
+    "purescript-assert": "4.0.0",
+    "purescript-bifunctors": "4.0.0",
+    "purescript-console": "4.1.0",
+    "purescript-control": "4.0.0",
+    "purescript-distributive": "4.0.0",
+    "purescript-effect": "2.0.0",
+    "purescript-either": "4.0.0",
+    "purescript-foldable-traversable": "4.0.0",
+    "purescript-functions": "4.0.0",
+    "purescript-gen": "2.0.0",
+    "purescript-generics-rep": "6.0.0",
+    "purescript-globals": "4.0.0",
+    "purescript-identity": "4.0.0",
+    "purescript-integers": "4.0.0",
+    "purescript-invariant": "4.0.0",
+    "purescript-lazy": "4.0.0",
+    "purescript-lists": "5.0.0",
+    "purescript-math": "2.1.1",
+    "purescript-maybe": "4.0.0",
+    "purescript-newtype": "3.0.0",
+    "purescript-nonempty": "5.0.0",
+    "purescript-partial": "2.0.0",
+    "purescript-prelude": "4.0.0",
+    "purescript-proxy": "3.0.0",
+    "purescript-psci-support": "4.0.0",
+    "purescript-refs": "4.1.0",
+    "purescript-st": "4.0.0",
+    "purescript-strings": "4.0.0",
+    "purescript-tailrec": "4.0.0",
+    "purescript-tuples": "5.0.0",
+    "purescript-type-equality": "3.0.0",
+    "purescript-typelevel-prelude": "3.0.0",
+    "purescript-unfoldable": "4.0.0",
+    "purescript-unsafe-coerce": "4.0.0"
   }
 }
diff --git a/tests/support/package-lock.json b/tests/support/package-lock.json
deleted file mode 100644
--- a/tests/support/package-lock.json
+++ /dev/null
@@ -1,171 +0,0 @@
-{
-  "requires": true,
-  "lockfileVersion": 1,
-  "dependencies": {
-    "bower": {
-      "version": "1.8.2",
-      "resolved": "https://registry.npmjs.org/bower/-/bower-1.8.2.tgz",
-      "integrity": "sha1-rfU1KcjUrwLvJPuNU0HBQZ0z4vc="
-    },
-    "fs.realpath": {
-      "version": "1.0.0",
-      "resolved": "https://registry.npmjs.org/fs.realpath/-/fs.realpath-1.0.0.tgz",
-      "integrity": "sha1-FQStJSMVjKpA20onh8sBQRmU6k8="
-    },
-    "glob": {
-      "version": "5.0.15",
-      "resolved": "https://registry.npmjs.org/glob/-/glob-5.0.15.tgz",
-      "integrity": "sha1-G8k2ueAvSmA/zCIuz3Yz0wuLk7E=",
-      "requires": {
-        "inflight": "1.0.6",
-        "inherits": "2.0.3",
-        "minimatch": "3.0.4",
-        "once": "1.4.0",
-        "path-is-absolute": "1.0.1"
-      },
-      "dependencies": {
-        "balanced-match": {
-          "version": "1.0.0",
-          "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.0.tgz",
-          "integrity": "sha1-ibTRmasr7kneFk6gK4nORi1xt2c="
-        },
-        "brace-expansion": {
-          "version": "1.1.11",
-          "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.11.tgz",
-          "integrity": "sha512-iCuPHDFgrHX7H2vEI/5xpz07zSHB00TpugqhmYtVmMO6518mCuRMoOYFldEBl0g187ufozdaHgWKcYFb61qGiA==",
-          "requires": {
-            "balanced-match": "1.0.0",
-            "concat-map": "0.0.1"
-          }
-        },
-        "concat-map": {
-          "version": "0.0.1",
-          "resolved": "https://registry.npmjs.org/concat-map/-/concat-map-0.0.1.tgz",
-          "integrity": "sha1-2Klr13/Wjfd5OnMDajug1UBdR3s="
-        },
-        "inflight": {
-          "version": "1.0.6",
-          "resolved": "https://registry.npmjs.org/inflight/-/inflight-1.0.6.tgz",
-          "integrity": "sha1-Sb1jMdfQLQwJvJEKEHW6gWW1bfk=",
-          "requires": {
-            "once": "1.4.0",
-            "wrappy": "1.0.2"
-          }
-        },
-        "inherits": {
-          "version": "2.0.3",
-          "resolved": "https://registry.npmjs.org/inherits/-/inherits-2.0.3.tgz",
-          "integrity": "sha1-Yzwsg+PaQqUC9SRmAiSA9CCCYd4="
-        },
-        "minimatch": {
-          "version": "3.0.4",
-          "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-3.0.4.tgz",
-          "integrity": "sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==",
-          "requires": {
-            "brace-expansion": "1.1.11"
-          }
-        },
-        "once": {
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diff --git a/tests/support/psci/Reload.edit b/tests/support/psci/Reload.edit
new file mode 100644
--- /dev/null
+++ b/tests/support/psci/Reload.edit
@@ -0,0 +1,4 @@
+module Reload where
+
+edited :: String
+edited = "reload"
diff --git a/tests/support/psci/Reload.purs b/tests/support/psci/Reload.purs
new file mode 100644
--- /dev/null
+++ b/tests/support/psci/Reload.purs
@@ -0,0 +1,4 @@
+module Reload where
+
+reload :: Int
+reload = 0
diff --git a/tests/support/psci/Sample.purs b/tests/support/psci/Sample.purs
deleted file mode 100644
--- a/tests/support/psci/Sample.purs
+++ /dev/null