diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,8 @@
 Changelog for HLint
 
+1.9.36
+    Require haskell-src-exts-1.18
+    #249, suggest avoiding elem on singletons
 1.9.35
     #245, fix parse error reports
     #243, update hlint.ghci to work with modern GHC
diff --git a/data/Default.hs b/data/Default.hs
--- a/data/Default.hs
+++ b/data/Default.hs
@@ -162,6 +162,8 @@
 warn = findIndices (a ==) ==> elemIndices a
 warn = findIndices (== a) ==> elemIndices a
 warn = lookup b (zip l [0..]) ==> elemIndex b l
+hint = elem x [y] ==> x == y where note = ValidInstance "Eq" a
+hint = notElem x [y] ==> x /= y where note = ValidInstance "Eq" a
 hint "Length always non-negative" = length x >= 0 ==> True
 hint "Use null" = length x > 0 ==> not (null x) where note = IncreasesLaziness
 hint "Use null" = length x >= 1 ==> not (null x) where note = IncreasesLaziness
diff --git a/hlint.cabal b/hlint.cabal
--- a/hlint.cabal
+++ b/hlint.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.8
 build-type:         Simple
 name:               hlint
-version:            1.9.35
+version:            1.9.36
 license:            BSD3
 license-file:       LICENSE
 category:           Development
@@ -49,7 +49,7 @@
         transformers,
         cpphs >= 1.20.1,
         cmdargs >= 0.10,
-        haskell-src-exts >= 1.17 && < 1.18,
+        haskell-src-exts >= 1.18 && < 1.19,
         uniplate >= 1.5,
         ansi-terminal >= 0.6.2,
         extra >= 1.4.9,
diff --git a/src/HSE/All.hs b/src/HSE/All.hs
--- a/src/HSE/All.hs
+++ b/src/HSE/All.hs
@@ -42,6 +42,7 @@
 parseFlagsNoLocations x = x{cppFlags = case cppFlags x of Cpphs y -> Cpphs $ f y; y -> y}
     where f x = x{boolopts = (boolopts x){locations=False}}
 
+-- | Given some fixities, add them to the existing fixities in 'ParseFlags'.
 parseFlagsAddFixities :: [Fixity] -> ParseFlags -> ParseFlags
 parseFlagsAddFixities fx x = x{hseFlags=hse{fixities = Just $ fx ++ fromMaybe [] (fixities hse)}}
     where hse = hseFlags x
@@ -127,8 +128,8 @@
         ask = askFixity fixs
 
         f o@(InfixApp s1 (InfixApp s2 x op1 y) op2 z)
-                | p1 == p2 && (a1 /= a2 || a1 == AssocNone) = o -- Ambiguous infix expression!
-                | p1 > p2 || p1 == p2 && (a1 == AssocLeft || a2 == AssocNone) = o
+                | p1 == p2 && (a1 /= a2 || isAssocNone a1) = o -- Ambiguous infix expression!
+                | p1 > p2 || p1 == p2 && (isAssocLeft a1 || isAssocNone a2) = o
                 | otherwise = InfixApp s1 x op1 (f $ InfixApp s1 y op2 z)
             where
                 (a1,p1) = ask op1
@@ -136,7 +137,7 @@
         f x = x
 
 
-askFixity :: [Fixity] -> QOp S -> (Assoc, Int)
-askFixity xs = \k -> Map.findWithDefault (AssocLeft, 9) (fromNamed k) mp
+askFixity :: [Fixity] -> QOp S -> (Assoc (), Int)
+askFixity xs = \k -> Map.findWithDefault (AssocLeft (), 9) (fromNamed k) mp
     where
-        mp = Map.fromList [(s,(a,p)) | Fixity a p x <- xs, let s = fromNamed x, s /= ""]
+        mp = Map.fromList [(s,(a,p)) | Fixity a p x <- xs, let s = fromNamed $ fmap (const an) x, s /= ""]
diff --git a/src/HSE/Match.hs b/src/HSE/Match.hs
--- a/src/HSE/Match.hs
+++ b/src/HSE/Match.hs
@@ -9,7 +9,6 @@
 import Data.Char
 import HSE.Type
 import HSE.Util
-import qualified Language.Haskell.Exts as HSE_
 
 
 class View a b where
@@ -87,15 +86,6 @@
     toNamed ":" = Special an $ Cons an
     toNamed x = UnQual an $ toNamed x
 
-instance Named HSE_.QName where
-    fromNamed (HSE_.Special HSE_.Cons) = ":"
-    fromNamed (HSE_.Special HSE_.UnitCon) = "()"
-    fromNamed (HSE_.UnQual x) = fromNamed x
-    fromNamed _ = ""
-
-    toNamed ":" = HSE_.Special HSE_.Cons
-    toNamed x = HSE_.UnQual $ toNamed x
-
 instance Named (Name S) where
     fromNamed (Ident _ x) = x
     fromNamed (Symbol _ x) = x
@@ -103,13 +93,6 @@
     toNamed x | isSym x = Symbol an x
               | otherwise = Ident an x
 
-instance Named HSE_.Name where
-    fromNamed (HSE_.Ident x) = x
-    fromNamed (HSE_.Symbol x) = x
-
-    toNamed x | isSym x = HSE_.Symbol x
-              | otherwise = HSE_.Ident x
-
 instance Named (ModuleName S) where
     fromNamed (ModuleName _ x) = x
     toNamed = ModuleName an
@@ -153,7 +136,7 @@
     fromNamed (TypeDecl _ name _) = fromNamed name
     fromNamed (DataDecl _ _ _ name _ _) = fromNamed name
     fromNamed (GDataDecl _ _ _ name _ _ _) = fromNamed name
-    fromNamed (TypeFamDecl _ name _) = fromNamed name
+    fromNamed (TypeFamDecl _ name _ _) = fromNamed name
     fromNamed (DataFamDecl _ _ name _) = fromNamed name
     fromNamed (ClassDecl _ _ name _ _) = fromNamed name
     fromNamed (PatBind _ (PVar _ name) _ _) = fromNamed name
diff --git a/src/HSE/Type.hs b/src/HSE/Type.hs
--- a/src/HSE/Type.hs
+++ b/src/HSE/Type.hs
@@ -3,8 +3,7 @@
 
 -- Almost all from the Annotated module, but the fixity resolution from Annotated
 -- uses the unannotated Assoc enumeration, so export that instead
-import Language.Haskell.Exts.Annotated as Export hiding (parse, loc, paren, Assoc(..))
-import Language.Haskell.Exts as Export(Assoc(..))
+import Language.Haskell.Exts as Export hiding (parse, loc, paren)
 import Data.Generics.Uniplate.Data as Export
 
 type S = SrcSpanInfo
diff --git a/src/HSE/Util.hs b/src/HSE/Util.hs
--- a/src/HSE/Util.hs
+++ b/src/HSE/Util.hs
@@ -7,7 +7,6 @@
 import Data.Maybe
 import System.FilePath
 import HSE.Type
-import Language.Haskell.Exts.Annotated.Simplify(sQName, sAssoc)
 import Prelude
 
 
@@ -150,6 +149,8 @@
 isLexeme Lit{} = True
 isLexeme _ = False
 
+isAssocLeft AssocLeft{} = True; isAssocLeft _ = False
+isAssocNone AssocNone{} = True; isAssocNone _ = False
 
 isWHNF :: Exp_ -> Bool
 isWHNF Con{} = True
@@ -312,7 +313,7 @@
 -- FIXITIES
 
 getFixity :: Decl a -> [Fixity]
-getFixity (InfixDecl sl a mp ops) = [Fixity (sAssoc a) (fromMaybe 9 mp) (sQName $ UnQual sl $ f op) | op <- ops]
+getFixity (InfixDecl sl a mp ops) = [Fixity (void a) (fromMaybe 9 mp) (UnQual () $ void $ f op) | op <- ops]
     where f (VarOp _ x) = x
           f (ConOp _ x) = x
 getFixity _ = []
diff --git a/src/Hint/All.hs b/src/Hint/All.hs
--- a/src/Hint/All.hs
+++ b/src/Hint/All.hs
@@ -62,10 +62,11 @@
 builtinHints :: [(String, Hint)]
 builtinHints = [(drop 4 $ show h, resolveHints [Left h]) | h <- [minBound .. maxBound]]
 
--- | Transform a list of 'HintRule' into a 'Hint'.
+-- | Transform a list of 'HintBuiltin' or 'HintRule' into a 'Hint'.
 resolveHints :: [Either HintBuiltin HintRule] -> Hint
 resolveHints xs = mconcat $ mempty{hintDecl=readMatch rights} : map builtin (nub lefts)
     where (lefts,rights) = partitionEithers xs
 
+-- | Transform a list of 'HintRule' into a 'Hint'.
 hintRules :: [HintRule] -> Hint
 hintRules = resolveHints . map Right
diff --git a/src/Hint/Pattern.hs b/src/Hint/Pattern.hs
--- a/src/Hint/Pattern.hs
+++ b/src/Hint/Pattern.hs
@@ -5,7 +5,7 @@
 
 <TEST>
 yes x y = if a then b else if c then d else e -- yes x y ; | a = b ; | c = d ; | otherwise = e
-x `yes` y = if a then b else if c then d else e -- yes x y ; | a = b ; | c = d ; | otherwise = e
+x `yes` y = if a then b else if c then d else e -- x `yes` y ; | a = b ; | c = d ; | otherwise = e
 no x y = if a then b else c
 -- foo b | c <- f b = c -- foo (f -> c) = c
 -- foo x y b z | c:cs <- f g b = c -- foo x y (f g -> c:cs) z = c
diff --git a/src/Language/Haskell/HLint2.hs b/src/Language/Haskell/HLint2.hs
--- a/src/Language/Haskell/HLint2.hs
+++ b/src/Language/Haskell/HLint2.hs
@@ -69,6 +69,7 @@
 autoSettings :: IO (ParseFlags, [Classify], Hint)
 autoSettings = getHLintDataDir >>= autoSettings'
 
+-- | Like 'autoSettings' but with a custom data directory.
 autoSettings' :: FilePath -> IO (ParseFlags, [Classify], Hint)
 autoSettings' dataDir = do
     (builtin, matches) <- first resolveBuiltin <$> findSettings dataDir (dataDir </> "HLint.hs") Nothing