diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -102,6 +102,7 @@
 | [@milesfrain](https://github.com/milesfrain) | Miles Frain | [MIT license] |
 | [@MiracleBlue](https://github.com/MiracleBlue) | Nicholas Kircher | [MIT license] |
 | [@mjgpy3](https://github.com/mjgpy3) | Michael Gilliland | [MIT license] |
+| [@mjrussell](https://github.com/mjrussell) | Matthew Russell | [MIT license] |
 | [@MonoidMusician](https://github.com/MonoidMusician) | Verity Scheel | [MIT license] |
 | [@mpietrzak](https://github.com/mpietrzak) | Maciej Pietrzak | [MIT license] |
 | [@mrhania](https://github.com/mrhania) | Łukasz Hanuszczak | [MIT license] |
diff --git a/purescript.cabal b/purescript.cabal
--- a/purescript.cabal
+++ b/purescript.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               purescript
-version:            0.15.13
+version:            0.15.14
 license:            BSD-3-Clause
 license-file:       LICENSE
 copyright:
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
@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveAnyClass #-}
 -- |
 -- Case binders
 --
@@ -5,6 +6,8 @@
 
 import Prelude
 
+import Control.DeepSeq (NFData)
+import GHC.Generics (Generic)
 import Language.PureScript.AST.SourcePos (SourceSpan)
 import Language.PureScript.AST.Literals (Literal(..))
 import Language.PureScript.Names (Ident, OpName, OpNameType(..), ProperName, ProperNameType(..), Qualified)
@@ -61,7 +64,7 @@
   -- A binder with a type annotation
   --
   | TypedBinder SourceType Binder
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- Manual Eq and Ord instances for `Binder` were added on 2018-03-05. Comparing
 -- the `SourceSpan` values embedded in some of the data constructors of `Binder`
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
@@ -50,7 +50,7 @@
     -- ^ Record fields that are available on the first argument to the typed
     -- hole
     }
-  deriving Show
+  deriving (Show, Generic, NFData)
 
 onTypeSearchTypes :: (SourceType -> SourceType) -> TypeSearch -> TypeSearch
 onTypeSearchTypes f = runIdentity . onTypeSearchTypesM (Identity . f)
@@ -90,7 +90,7 @@
   | MissingConstructorImportForCoercible (Qualified (ProperName 'ConstructorName))
   | PositionedError (NEL.NonEmpty SourceSpan)
   | RelatedPositions (NEL.NonEmpty SourceSpan)
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- | Categories of hints
 data HintCategory
@@ -105,14 +105,14 @@
 
 -- |
 -- In constraint solving, indicates whether there were `TypeUnknown`s that prevented
--- an instance from being found, and whether VTAs are required 
+-- an instance from being found, and whether VTAs are required
 -- due to type class members not referencing all the type class
 -- head's type variables.
 data UnknownsHint
   = NoUnknowns
   | Unknowns
   | UnknownsWithVtaRequiringArgs (NEL.NonEmpty (Qualified Ident, [[Text]]))
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- |
 -- A module declaration, consisting of comments about the module, a module name,
@@ -306,7 +306,7 @@
   -- An import with a list of references to hide: `import M hiding (foo)`
   --
   | Hiding [DeclarationRef]
-  deriving (Eq, Show, Generic, Serialise)
+  deriving (Eq, Show, Generic, Serialise, NFData)
 
 isExplicit :: ImportDeclarationType -> Bool
 isExplicit (Explicit _) = True
@@ -323,7 +323,7 @@
   { rdeclSourceAnn :: !SourceAnn
   , rdeclIdent :: !(ProperName 'TypeName)
   , rdeclRoles :: ![Role]
-  } deriving (Show, Eq)
+  } deriving (Show, Eq, Generic, NFData)
 
 -- | A type declaration assigns a type to an identifier, eg:
 --
@@ -334,7 +334,7 @@
   { tydeclSourceAnn :: !SourceAnn
   , tydeclIdent :: !Ident
   , tydeclType :: !SourceType
-  } deriving (Show, Eq)
+  } deriving (Show, Eq, Generic, NFData)
 
 getTypeDeclaration :: Declaration -> Maybe TypeDeclarationData
 getTypeDeclaration (TypeDeclaration d) = Just d
@@ -356,7 +356,7 @@
   -- ^ Whether or not this value is exported/visible
   , valdeclBinders :: ![Binder]
   , valdeclExpression :: !a
-  } deriving (Show, Functor, Foldable, Traversable)
+  } deriving (Show, Functor, Generic, NFData, Foldable, Traversable)
 
 getValueDeclaration :: Declaration -> Maybe (ValueDeclarationData [GuardedExpr])
 getValueDeclaration (ValueDeclaration d) = Just d
@@ -370,7 +370,7 @@
   { dataCtorAnn :: !SourceAnn
   , dataCtorName :: !(ProperName 'ConstructorName)
   , dataCtorFields :: ![(Ident, SourceType)]
-  } deriving (Show, Eq)
+  } deriving (Show, Eq, Generic, NFData)
 
 mapDataCtorFields :: ([(Ident, SourceType)] -> [(Ident, SourceType)]) -> DataConstructorDeclaration -> DataConstructorDeclaration
 mapDataCtorFields f DataConstructorDeclaration{..} = DataConstructorDeclaration { dataCtorFields = f dataCtorFields, .. }
@@ -445,13 +445,13 @@
   -- declaration, while the second @SourceAnn@ serves as the
   -- annotation for the type class and its arguments.
   | TypeInstanceDeclaration SourceAnn SourceAnn ChainId Integer (Either Text Ident) [SourceConstraint] (Qualified (ProperName 'ClassName)) [SourceType] TypeInstanceBody
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 data ValueFixity = ValueFixity Fixity (Qualified (Either Ident (ProperName 'ConstructorName))) (OpName 'ValueOpName)
-  deriving (Eq, Ord, Show)
+  deriving (Eq, Ord, Show, Generic, NFData)
 
 data TypeFixity = TypeFixity Fixity (Qualified (ProperName 'TypeName)) (OpName 'TypeOpName)
-  deriving (Eq, Ord, Show)
+  deriving (Eq, Ord, Show, Generic, NFData)
 
 pattern ValueFixityDeclaration :: SourceAnn -> Fixity -> Qualified (Either Ident (ProperName 'ConstructorName)) -> OpName 'ValueOpName -> Declaration
 pattern ValueFixityDeclaration sa fixity name op = FixityDeclaration sa (Left (ValueFixity fixity name op))
@@ -462,7 +462,7 @@
 data InstanceDerivationStrategy
   = KnownClassStrategy
   | NewtypeStrategy
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- | The members of a type class instance declaration
 data TypeInstanceBody
@@ -472,7 +472,7 @@
   -- ^ This is an instance derived from a newtype
   | ExplicitInstance [Declaration]
   -- ^ This is a regular (explicit) instance
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 mapTypeInstanceBody :: ([Declaration] -> [Declaration]) -> TypeInstanceBody -> TypeInstanceBody
 mapTypeInstanceBody f = runIdentity . traverseTypeInstanceBody (Identity . f)
@@ -488,9 +488,7 @@
   | NewtypeSig
   | TypeSynonymSig
   | ClassSig
-  deriving (Eq, Ord, Show, Generic)
-
-instance NFData KindSignatureFor
+  deriving (Eq, Ord, Show, Generic, NFData)
 
 declSourceAnn :: Declaration -> SourceAnn
 declSourceAnn (DataDeclaration sa _ _ _ _) = sa
@@ -627,13 +625,13 @@
 --
 data Guard = ConditionGuard Expr
            | PatternGuard Binder Expr
-           deriving (Show)
+           deriving (Show, Generic, NFData)
 
 -- |
 -- The right hand side of a binder in value declarations
 -- and case expressions.
 data GuardedExpr = GuardedExpr [Guard] Expr
-                 deriving (Show)
+                 deriving (Show, Generic, NFData)
 
 pattern MkUnguarded :: Expr -> GuardedExpr
 pattern MkUnguarded e = GuardedExpr [] e
@@ -764,7 +762,7 @@
   -- A value with source position information
   --
   | PositionedValue SourceSpan [Comment] Expr
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- |
 -- Metadata that tells where a let binding originated
@@ -778,7 +776,7 @@
   -- The let binding was always a let binding
   --
   | FromLet
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- |
 -- An alternative in a case statement
@@ -792,7 +790,7 @@
     -- The result expression or a collect of guarded expressions
     --
   , caseAlternativeResult :: [GuardedExpr]
-  } deriving (Show)
+  } deriving (Show, Generic, NFData)
 
 -- |
 -- A statement in a do-notation block
@@ -814,7 +812,7 @@
   -- A do notation element with source position information
   --
   | PositionedDoNotationElement SourceSpan [Comment] DoNotationElement
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 
 -- For a record update such as:
@@ -842,12 +840,14 @@
 
 newtype PathTree t = PathTree (AssocList PSString (PathNode t))
   deriving (Show, Eq, Ord, Functor, Foldable, Traversable)
+  deriving newtype NFData
 
 data PathNode t = Leaf t | Branch (PathTree t)
-  deriving (Show, Eq, Ord, Functor, Foldable, Traversable)
+  deriving (Show, Eq, Ord, Generic, NFData, Functor, Foldable, Traversable)
 
 newtype AssocList k t = AssocList { runAssocList :: [(k, t)] }
   deriving (Show, Eq, Ord, Foldable, Functor, Traversable)
+  deriving newtype NFData
 
 $(deriveJSON (defaultOptions { sumEncoding = ObjectWithSingleField }) ''NameSource)
 $(deriveJSON (defaultOptions { sumEncoding = ObjectWithSingleField }) ''ExportSource)
diff --git a/src/Language/PureScript/AST/Literals.hs b/src/Language/PureScript/AST/Literals.hs
--- a/src/Language/PureScript/AST/Literals.hs
+++ b/src/Language/PureScript/AST/Literals.hs
@@ -1,9 +1,12 @@
+{-# LANGUAGE DeriveAnyClass #-}
 -- |
 -- The core functional representation for literal values.
 --
 module Language.PureScript.AST.Literals where
 
 import Prelude
+import Control.DeepSeq (NFData)
+import GHC.Generics (Generic)
 import Language.PureScript.PSString (PSString)
 
 -- |
@@ -35,4 +38,4 @@
   -- An object literal
   --
   | ObjectLiteral [(PSString, a)]
-  deriving (Eq, Ord, Show, Functor)
+  deriving (Eq, Ord, Show, Functor, Generic, NFData)
diff --git a/src/Language/PureScript/Bundle.hs b/src/Language/PureScript/Bundle.hs
--- a/src/Language/PureScript/Bundle.hs
+++ b/src/Language/PureScript/Bundle.hs
@@ -4,6 +4,7 @@
 -- This module takes as input the individual generated modules from 'Language.PureScript.Make' and
 -- performs dead code elimination, filters empty modules,
 -- and generates the final JavaScript bundle.
+{-# LANGUAGE DeriveAnyClass #-}
 module Language.PureScript.Bundle
   ( ModuleIdentifier(..)
   , ModuleType(..)
@@ -18,6 +19,7 @@
 
 import Prelude
 
+import Control.DeepSeq (NFData)
 import Control.Monad.Error.Class (MonadError(..))
 
 import Data.Aeson ((.=))
@@ -27,6 +29,8 @@
 import Data.Aeson qualified as A
 import Data.Text.Lazy qualified as LT
 
+import GHC.Generics (Generic)
+
 import Language.JavaScript.Parser (JSAST(..), JSAnnot(..), JSAssignOp(..), JSExpression(..), JSStatement(..), renderToText)
 import Language.JavaScript.Parser.AST (JSCommaList(..), JSCommaTrailingList(..), JSExportClause(..), JSExportDeclaration(..), JSExportSpecifier(..), JSFromClause(..), JSIdent(..), JSImportDeclaration(..), JSModuleItem(..), JSObjectProperty(..), JSObjectPropertyList, JSPropertyName(..), JSVarInitializer(..))
 import Language.JavaScript.Process.Minify (minifyJS)
@@ -42,21 +46,22 @@
   | ErrorInModule ModuleIdentifier ErrorMessage
   | MissingEntryPoint String
   | MissingMainModule String
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 -- | Modules are either "regular modules" (i.e. those generated by the PureScript compiler) or
 -- foreign modules.
 data ModuleType
   = Regular
   | Foreign
-  deriving (Show, Eq, Ord)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 showModuleType :: ModuleType -> String
 showModuleType Regular = "Regular"
 showModuleType Foreign = "Foreign"
 
 -- | A module is identified by its module name and its type.
-data ModuleIdentifier = ModuleIdentifier String ModuleType deriving (Show, Eq, Ord)
+data ModuleIdentifier = ModuleIdentifier String ModuleType
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 instance A.ToJSON ModuleIdentifier where
   toJSON (ModuleIdentifier name mt) =
diff --git a/src/Language/PureScript/CST/Errors.hs b/src/Language/PureScript/CST/Errors.hs
--- a/src/Language/PureScript/CST/Errors.hs
+++ b/src/Language/PureScript/CST/Errors.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveAnyClass #-}
 module Language.PureScript.CST.Errors
   ( ParserErrorInfo(..)
   , ParserErrorType(..)
@@ -11,8 +12,10 @@
 
 import Prelude
 
+import Control.DeepSeq (NFData)
 import Data.Text qualified as Text
 import Data.Char (isSpace, toUpper)
+import GHC.Generics (Generic)
 import Language.PureScript.CST.Layout (LayoutStack)
 import Language.PureScript.CST.Print (printToken)
 import Language.PureScript.CST.Types (SourcePos(..), SourceRange(..), SourceToken(..), Token(..))
@@ -56,7 +59,7 @@
   | ErrConstraintInForeignImportSyntax
   | ErrEof
   | ErrCustom String
-  deriving (Show, Eq, Ord)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 data ParserWarningType
   = WarnDeprecatedRowSyntax
@@ -64,14 +67,14 @@
   | WarnDeprecatedKindImportSyntax
   | WarnDeprecatedKindExportSyntax
   | WarnDeprecatedCaseOfOffsideSyntax
-  deriving (Show, Eq, Ord)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 data ParserErrorInfo a = ParserErrorInfo
   { errRange :: SourceRange
   , errToks :: [SourceToken]
   , errStack :: LayoutStack
   , errType :: a
-  } deriving (Show, Eq)
+  } deriving (Show, Eq, Generic, NFData)
 
 type ParserError = ParserErrorInfo ParserErrorType
 type ParserWarning = ParserErrorInfo ParserWarningType
diff --git a/src/Language/PureScript/CST/Layout.hs b/src/Language/PureScript/CST/Layout.hs
--- a/src/Language/PureScript/CST/Layout.hs
+++ b/src/Language/PureScript/CST/Layout.hs
@@ -166,14 +166,17 @@
 --    "body of a case of expression" by pushing 'LytOf' onto the layout stack.
 --    Insert the @of@ token into the stream of tokens.
 --
+{-# LANGUAGE DeriveAnyClass #-}
 module Language.PureScript.CST.Layout where
 
 import Prelude
 
+import Control.DeepSeq (NFData)
 import Data.DList (snoc)
 import Data.DList qualified as DList
 import Data.Foldable (find)
 import Data.Function ((&))
+import GHC.Generics (Generic)
 import Language.PureScript.CST.Types (Comment, LineFeed, SourcePos(..), SourceRange(..), SourceToken(..), Token(..), TokenAnn(..))
 
 type LayoutStack = [(SourcePos, LayoutDelim)]
@@ -201,7 +204,7 @@
   | LytOf
   | LytDo
   | LytAdo
-  deriving (Show, Eq, Ord)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 isIndented :: LayoutDelim -> Bool
 isIndented = \case
diff --git a/src/Language/PureScript/CST/Parser.y b/src/Language/PureScript/CST/Parser.y
--- a/src/Language/PureScript/CST/Parser.y
+++ b/src/Language/PureScript/CST/Parser.y
@@ -722,7 +722,7 @@
   : constraints '<=' {%^ revert $ pure ($1, $2) }
 
 classNameAndFundeps :: { (Name (N.ProperName 'N.ClassName), [TypeVarBinding ()], Maybe (SourceToken, Separated ClassFundep)) }
-  : properName manyOrEmpty(typeVarBinding) fundeps {%^ revert $ pure (getProperName $1, $2, $3) }
+  : properName manyOrEmpty(typeVarBindingPlain) fundeps {%^ revert $ pure (getProperName $1, $2, $3) }
 
 fundeps :: { Maybe (SourceToken, Separated ClassFundep) }
   : {- empty -} { Nothing }
diff --git a/src/Language/PureScript/CST/Types.hs b/src/Language/PureScript/CST/Types.hs
--- a/src/Language/PureScript/CST/Types.hs
+++ b/src/Language/PureScript/CST/Types.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveAnyClass #-}
 -- | This module contains data types for the entire PureScript surface language. Every
 -- token is represented in the tree, and every token is annotated with
 -- whitespace and comments (both leading and trailing). This means one can write
@@ -9,6 +10,7 @@
 
 import Prelude
 
+import Control.DeepSeq (NFData)
 import Data.List.NonEmpty (NonEmpty)
 import Data.Text (Text)
 import Data.Void (Void)
@@ -20,30 +22,30 @@
 data SourcePos = SourcePos
   { srcLine :: {-# UNPACK #-} !Int
   , srcColumn :: {-# UNPACK #-} !Int
-  } deriving (Show, Eq, Ord, Generic)
+  } deriving (Show, Eq, Ord, Generic, NFData)
 
 data SourceRange = SourceRange
   { srcStart :: !SourcePos
   , srcEnd :: !SourcePos
-  } deriving (Show, Eq, Ord, Generic)
+  } deriving (Show, Eq, Ord, Generic, NFData)
 
 data Comment l
   = Comment !Text
   | Space {-# UNPACK #-} !Int
   | Line !l
-  deriving (Show, Eq, Ord, Generic, Functor)
+  deriving (Show, Eq, Ord, Generic, Functor, NFData)
 
 data LineFeed = LF | CRLF
-  deriving (Show, Eq, Ord, Generic)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 data TokenAnn = TokenAnn
   { tokRange :: !SourceRange
   , tokLeadingComments :: ![Comment LineFeed]
   , tokTrailingComments :: ![Comment Void]
-  } deriving (Show, Eq, Ord, Generic)
+  } deriving (Show, Eq, Ord, Generic, NFData)
 
 data SourceStyle = ASCII | Unicode
-  deriving (Show, Eq, Ord, Generic)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 data Token
   = TokLeftParen
@@ -79,12 +81,12 @@
   | TokLayoutSep
   | TokLayoutEnd
   | TokEof
-  deriving (Show, Eq, Ord, Generic)
+  deriving (Show, Eq, Ord, Generic, NFData)
 
 data SourceToken = SourceToken
   { tokAnn :: !TokenAnn
   , tokValue :: !Token
-  } deriving (Show, Eq, Ord, Generic)
+  } deriving (Show, Eq, Ord, Generic, NFData)
 
 data Ident = Ident
   { getIdent :: Text
diff --git a/src/Language/PureScript/CoreFn/CSE.hs b/src/Language/PureScript/CoreFn/CSE.hs
--- a/src/Language/PureScript/CoreFn/CSE.hs
+++ b/src/Language/PureScript/CoreFn/CSE.hs
@@ -12,7 +12,7 @@
 import Data.Functor.Compose (Compose(..))
 import Data.IntMap.Monoidal qualified as IM
 import Data.IntSet qualified as IS
-import Data.Map qualified as M
+import Data.Map.Strict qualified as M
 import Data.Maybe (fromJust)
 import Data.Semigroup (Min(..))
 import Data.Semigroup.Generic (GenericSemigroupMonoid(..))
@@ -216,7 +216,7 @@
     if isTopLevel
     then env{ _depth = depth', _deepestTopLevelScope = depth' }
     else env{ _depth = depth' }
-    where 
+    where
     depth' = succ _depth
 
 -- |
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
@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveAnyClass #-}
 module Language.PureScript.Errors
   ( module Language.PureScript.AST
   , module Language.PureScript.Errors
@@ -7,7 +8,7 @@
 import Protolude (unsnoc)
 
 import Control.Arrow ((&&&))
-import Control.Exception (displayException)
+import Control.DeepSeq (NFData)
 import Control.Lens (both, head1, over)
 import Control.Monad (forM, unless)
 import Control.Monad.Error.Class (MonadError(..))
@@ -32,6 +33,7 @@
 import Data.Text qualified as T
 import Data.Text (Text)
 import Data.Traversable (for)
+import GHC.Generics (Generic)
 import GHC.Stack qualified
 import Language.PureScript.AST
 import Language.PureScript.Bundle qualified as Bundle
@@ -70,7 +72,7 @@
   | DeprecatedFFICommonJSModule ModuleName FilePath
   | UnsupportedFFICommonJSExports ModuleName [Text]
   | UnsupportedFFICommonJSImports ModuleName [Text]
-  | FileIOError Text IOError -- ^ A description of what we were trying to do, and the error which occurred
+  | FileIOError Text Text -- ^ A description of what we were trying to do, and the error which occurred
   | InfiniteType SourceType
   | InfiniteKind SourceType
   | MultipleValueOpFixities (OpName 'ValueOpName)
@@ -196,12 +198,12 @@
   | CannotDeriveInvalidConstructorArg (Qualified (ProperName 'ClassName)) [Qualified (ProperName 'ClassName)] Bool
   | CannotSkipTypeApplication SourceType
   | CannotApplyExpressionOfTypeOnType SourceType SourceType
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 data ErrorMessage = ErrorMessage
   [ErrorMessageHint]
   SimpleErrorMessage
-  deriving (Show)
+  deriving (Show, Generic, NFData)
 
 newtype ErrorSuggestion = ErrorSuggestion Text
 
@@ -369,7 +371,9 @@
 -- | A stack trace for an error
 newtype MultipleErrors = MultipleErrors
   { runMultipleErrors :: [ErrorMessage]
-  } deriving (Show, Semigroup, Monoid)
+  }
+  deriving stock (Show)
+  deriving newtype (Semigroup, Monoid, NFData)
 
 -- | Check whether a collection of errors is empty or not.
 nonEmpty :: MultipleErrors -> Bool
@@ -679,7 +683,7 @@
             ]
     renderSimpleErrorMessage (FileIOError doWhat err) =
       paras [ line $ "I/O error while trying to " <> doWhat
-            , indent . lineS $ displayException err
+            , indent . line $ err
             ]
     renderSimpleErrorMessage (ErrorParsingFFIModule path extra) =
       paras $ [ line "Unable to parse foreign module:"
@@ -941,7 +945,7 @@
                           <> case argsRequiringVtas of
                               [required] ->
                                 [ Box.moveRight 2 $ line $ T.intercalate ", " required ]
-                              options -> 
+                              options ->
                                 [ Box.moveRight 2 $ line "One of the following sets of type variables:"
                                 , Box.moveRight 2 $ paras $
                                     map (\set -> Box.moveRight 2 $ line $ T.intercalate ", " set) options
diff --git a/src/Language/PureScript/Externs.hs b/src/Language/PureScript/Externs.hs
--- a/src/Language/PureScript/Externs.hs
+++ b/src/Language/PureScript/Externs.hs
@@ -1,3 +1,4 @@
+{-# Language DeriveAnyClass #-}
 -- |
 -- This module generates code for \"externs\" files, i.e. files containing only
 -- foreign import declarations.
@@ -17,8 +18,8 @@
 import Prelude
 
 import Codec.Serialise (Serialise)
+import Control.DeepSeq (NFData)
 import Control.Monad (join)
-import GHC.Generics (Generic)
 import Data.Maybe (fromMaybe, mapMaybe, maybeToList)
 import Data.List (foldl', find)
 import Data.Foldable (fold)
@@ -27,6 +28,7 @@
 import Data.Version (showVersion)
 import Data.Map qualified as M
 import Data.List.NonEmpty qualified as NEL
+import GHC.Generics (Generic)
 
 import Language.PureScript.AST (Associativity, Declaration(..), DeclarationRef(..), Fixity(..), ImportDeclarationType, Module(..), NameSource(..), Precedence, SourceSpan, pattern TypeFixityDeclaration, pattern ValueFixityDeclaration, getTypeOpRef, getValueOpRef)
 import Language.PureScript.AST.Declarations.ChainId (ChainId)
@@ -59,7 +61,7 @@
   -- ^ List of type and value declaration
   , efSourceSpan :: SourceSpan
   -- ^ Source span for error reporting
-  } deriving (Show, Generic)
+  } deriving (Show, Generic, NFData)
 
 instance Serialise ExternsFile
 
@@ -72,7 +74,7 @@
   , eiImportType :: ImportDeclarationType
   -- | The imported-as name, for qualified imports
   , eiImportedAs :: Maybe ModuleName
-  } deriving (Show, Generic)
+  } deriving (Show, Generic, NFData)
 
 instance Serialise ExternsImport
 
@@ -87,7 +89,7 @@
   , efOperator :: OpName 'ValueOpName
   -- | The value the operator is an alias for
   , efAlias :: Qualified (Either Ident (ProperName 'ConstructorName))
-  } deriving (Show, Generic)
+  } deriving (Show, Generic, NFData)
 
 instance Serialise ExternsFixity
 
@@ -102,7 +104,7 @@
   , efTypeOperator :: OpName 'TypeOpName
   -- | The value the operator is an alias for
   , efTypeAlias :: Qualified (ProperName 'TypeName)
-  } deriving (Show, Generic)
+  } deriving (Show, Generic, NFData)
 
 instance Serialise ExternsTypeFixity
 
@@ -155,7 +157,7 @@
       , edInstanceNameSource      :: NameSource
       , edInstanceSourceSpan      :: SourceSpan
       }
-  deriving (Show, Generic)
+  deriving (Show, Generic, NFData)
 
 instance Serialise ExternsDeclaration
 
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
@@ -12,12 +12,14 @@
 import Prelude
 
 import Control.Concurrent.Lifted as C
-import Control.Exception.Base (onException)
-import Control.Monad (foldM, unless, when)
+import Control.DeepSeq (force)
+import Control.Exception.Lifted (onException, bracket_, evaluate)
+import Control.Monad (foldM, unless, when, (<=<))
+import Control.Monad.Base (MonadBase(liftBase))
 import Control.Monad.Error.Class (MonadError(..))
 import Control.Monad.IO.Class (MonadIO(..))
 import Control.Monad.Supply (evalSupplyT, runSupply, runSupplyT)
-import Control.Monad.Trans.Control (MonadBaseControl(..), control)
+import Control.Monad.Trans.Control (MonadBaseControl(..))
 import Control.Monad.Trans.State (runStateT)
 import Control.Monad.Writer.Class (MonadWriter(..), censor)
 import Control.Monad.Writer.Strict (runWriterT)
@@ -29,6 +31,7 @@
 import Data.Map qualified as M
 import Data.Set qualified as S
 import Data.Text qualified as T
+import Debug.Trace (traceMarkerIO)
 import Language.PureScript.AST (ErrorMessageHint(..), Module(..), SourceSpan(..), getModuleName, getModuleSourceSpan, importPrim)
 import Language.PureScript.Crash (internalError)
 import Language.PureScript.CST qualified as CST
@@ -56,7 +59,7 @@
 -- This function is used for fast-rebuild workflows (PSCi and psc-ide are examples).
 rebuildModule
   :: forall m
-   . (MonadBaseControl IO m, MonadError MultipleErrors m, MonadWriter MultipleErrors m)
+   . (MonadError MultipleErrors m, MonadWriter MultipleErrors m)
   => MakeActions m
   -> [ExternsFile]
   -> Module
@@ -67,7 +70,7 @@
 
 rebuildModule'
   :: forall m
-   . (MonadBaseControl IO m, MonadError MultipleErrors m, MonadWriter MultipleErrors m)
+   . (MonadError MultipleErrors m, MonadWriter MultipleErrors m)
   => MakeActions m
   -> Env
   -> [ExternsFile]
@@ -77,7 +80,7 @@
 
 rebuildModuleWithIndex
   :: forall m
-   . (MonadBaseControl IO m, MonadError MultipleErrors m, MonadWriter MultipleErrors m)
+   . (MonadError MultipleErrors m, MonadWriter MultipleErrors m)
   => MakeActions m
   -> Env
   -> [ExternsFile]
@@ -148,12 +151,21 @@
 
   (buildPlan, newCacheDb) <- BuildPlan.construct ma cacheDb (sorted, graph)
 
+  -- Limit concurrent module builds to the number of capabilities as
+  -- (by default) inferred from `+RTS -N -RTS` or set explicitly like `-N4`.
+  -- This is to ensure that modules complete fully before moving on, to avoid
+  -- holding excess memory during compilation from modules that were paused
+  -- by the Haskell runtime.
+  capabilities <- getNumCapabilities
+  let concurrency = max 1 capabilities
+  lock <- C.newQSem concurrency
+
   let toBeRebuilt = filter (BuildPlan.needsRebuild buildPlan . getModuleName . CST.resPartial) sorted
   let totalModuleCount = length toBeRebuilt
   for_ toBeRebuilt $ \m -> fork $ do
     let moduleName = getModuleName . CST.resPartial $ m
     let deps = fromMaybe (internalError "make: module not found in dependency graph.") (lookup moduleName graph)
-    buildModule buildPlan moduleName totalModuleCount
+    buildModule lock buildPlan moduleName totalModuleCount
       (spanName . getModuleSourceSpan . CST.resPartial $ m)
       (fst $ CST.resFull m)
       (fmap importPrim . snd $ CST.resFull m)
@@ -161,7 +173,7 @@
 
       -- Prevent hanging on other modules when there is an internal error
       -- (the exception is thrown, but other threads waiting on MVars are released)
-      `onExceptionLifted` BuildPlan.markComplete buildPlan moduleName (BuildJobFailed mempty)
+      `onException` BuildPlan.markComplete buildPlan moduleName (BuildJobFailed mempty)
 
   -- Wait for all threads to complete, and collect results (and errors).
   (failures, successes) <-
@@ -227,8 +239,8 @@
   inOrderOf :: (Ord a) => [a] -> [a] -> [a]
   inOrderOf xs ys = let s = S.fromList xs in filter (`S.member` s) ys
 
-  buildModule :: BuildPlan -> ModuleName -> Int -> FilePath -> [CST.ParserWarning] -> Either (NEL.NonEmpty CST.ParserError) Module -> [ModuleName] -> m ()
-  buildModule buildPlan moduleName cnt fp pwarnings mres deps = do
+  buildModule :: QSem -> BuildPlan -> ModuleName -> Int -> FilePath -> [CST.ParserWarning] -> Either (NEL.NonEmpty CST.ParserError) Module -> [ModuleName] -> m ()
+  buildModule lock buildPlan moduleName cnt fp pwarnings mres deps = do
     result <- flip catchError (return . BuildJobFailed) $ do
       let pwarnings' = CST.toMultipleWarnings fp pwarnings
       tell pwarnings'
@@ -252,14 +264,23 @@
           env <- C.readMVar (bpEnv buildPlan)
           idx <- C.takeMVar (bpIndex buildPlan)
           C.putMVar (bpIndex buildPlan) (idx + 1)
-          (exts, warnings) <- listen $ rebuildModuleWithIndex ma env externs m (Just (idx, cnt))
+
+          -- Bracket all of the per-module work behind the semaphore, including
+          -- forcing the result. This is done to limit concurrency and keep
+          -- memory usage down; see comments above.
+          (exts, warnings) <- bracket_ (C.waitQSem lock) (C.signalQSem lock) $ do
+            -- Eventlog markers for profiling; see debug/eventlog.js
+            liftBase $ traceMarkerIO $ T.unpack (runModuleName moduleName) <> " start"
+            -- Force the externs and warnings to avoid retaining excess module
+            -- data after the module is finished compiling.
+            extsAndWarnings <- evaluate . force <=< listen $ do
+              rebuildModuleWithIndex ma env externs m (Just (idx, cnt))
+            liftBase $ traceMarkerIO $ T.unpack (runModuleName moduleName) <> " end"
+            return extsAndWarnings
           return $ BuildJobSucceeded (pwarnings' <> warnings) exts
         Nothing -> return BuildJobSkipped
 
     BuildPlan.markComplete buildPlan moduleName result
-
-  onExceptionLifted :: m a -> m b -> m a
-  onExceptionLifted l r = control $ \runInIO -> runInIO l `onException` runInIO r
 
 -- | Infer the module name for a module by looking for the same filename with
 -- a .js extension.
diff --git a/src/Language/PureScript/Make/Monad.hs b/src/Language/PureScript/Make/Monad.hs
--- a/src/Language/PureScript/Make/Monad.hs
+++ b/src/Language/PureScript/Make/Monad.hs
@@ -23,7 +23,7 @@
 
 import Codec.Serialise (Serialise)
 import Codec.Serialise qualified as Serialise
-import Control.Exception (fromException, tryJust)
+import Control.Exception (fromException, tryJust, Exception (displayException))
 import Control.Monad (join, guard)
 import Control.Monad.Base (MonadBase(..))
 import Control.Monad.Error.Class (MonadError(..))
@@ -71,7 +71,7 @@
 makeIO :: (MonadIO m, MonadError MultipleErrors m) => Text -> IO a -> m a
 makeIO description io = do
   res <- liftIO (tryIOError io)
-  either (throwError . singleError . ErrorMessage [] . FileIOError description) pure res
+  either (throwError . singleError . ErrorMessage [] . FileIOError description . Text.pack . displayException) pure res
 
 -- | Get a file's modification time in the 'Make' monad, capturing any errors
 -- using the 'MonadError' instance.
diff --git a/tests/purs/failing/4522.out b/tests/purs/failing/4522.out
new file mode 100644
--- /dev/null
+++ b/tests/purs/failing/4522.out
@@ -0,0 +1,10 @@
+Error found:
+at tests/purs/failing/4522.purs:4:11 - 4:12 (line 4, column 11 - line 4, column 12)
+
+  Unable to parse module:
+  Unexpected token '@'
+
+
+See https://github.com/purescript/documentation/blob/master/errors/ErrorParsingModule.md for more information,
+or to contribute content related to this error.
+
diff --git a/tests/purs/failing/4522.purs b/tests/purs/failing/4522.purs
new file mode 100644
--- /dev/null
+++ b/tests/purs/failing/4522.purs
@@ -0,0 +1,4 @@
+-- @shouldFailWith ErrorParsingModule
+module Main where
+
+class Foo @a
diff --git a/tests/support/package-lock.json b/tests/support/package-lock.json
--- a/tests/support/package-lock.json
+++ b/tests/support/package-lock.json
@@ -17,9 +17,9 @@
       "integrity": "sha512-3oSeUO0TMV67hN1AmbXsK4yaqU7tjiHlbxRDZOpH0KW9+CeX4bRAaX0Anxt0tx2MrpRpWwQaPwIlISEJhYU5Pw=="
     },
     "node_modules/bower": {
-      "version": "1.8.13",
-      "resolved": "https://registry.npmjs.org/bower/-/bower-1.8.13.tgz",
-      "integrity": "sha512-8eWko16JlCTdaZZG70kddHPed17pHEbH8/IjfP4IFkQsfEqRsyNM09Dc8cDBFkSvtQ/2lTea7A+bMhRggG2a+Q==",
+      "version": "1.8.14",
+      "resolved": "https://registry.npmjs.org/bower/-/bower-1.8.14.tgz",
+      "integrity": "sha512-8Rq058FD91q9Nwthyhw0la9fzpBz0iwZTrt51LWl+w+PnJgZk9J+5wp3nibsJcIUPglMYXr4NRBaR+TUj0OkBQ==",
       "bin": {
         "bower": "bin/bower"
       },
@@ -153,9 +153,9 @@
       "integrity": "sha512-3oSeUO0TMV67hN1AmbXsK4yaqU7tjiHlbxRDZOpH0KW9+CeX4bRAaX0Anxt0tx2MrpRpWwQaPwIlISEJhYU5Pw=="
     },
     "bower": {
-      "version": "1.8.13",
-      "resolved": "https://registry.npmjs.org/bower/-/bower-1.8.13.tgz",
-      "integrity": "sha512-8eWko16JlCTdaZZG70kddHPed17pHEbH8/IjfP4IFkQsfEqRsyNM09Dc8cDBFkSvtQ/2lTea7A+bMhRggG2a+Q=="
+      "version": "1.8.14",
+      "resolved": "https://registry.npmjs.org/bower/-/bower-1.8.14.tgz",
+      "integrity": "sha512-8Rq058FD91q9Nwthyhw0la9fzpBz0iwZTrt51LWl+w+PnJgZk9J+5wp3nibsJcIUPglMYXr4NRBaR+TUj0OkBQ=="
     },
     "brace-expansion": {
       "version": "1.1.11",