Trim unused imports detected by new unused-import code

[ghc-hetmet.git] / compiler / types / TypeRep.lhs

diff --git a/compiler/types/TypeRep.lhs b/compiler/types/TypeRep.lhs
index 52e12bf..146c081 100644 (file)
--- a/compiler/types/TypeRep.lhs
+++ b/compiler/types/TypeRep.lhs
@@ -15,7 +15,7 @@ module TypeRep (
        
        Kind, ThetaType,                -- Synonyms
 
-       funTyCon,
+       funTyCon, funTyConName,
 
        -- Pretty-printing
        pprType, pprParendType, pprTypeApp,
@@ -53,7 +53,6 @@ import {-# SOURCE #-} DataCon( DataCon, dataConName )
 -- friends:
 import Var
 import Name
-import OccName
 import BasicTypes
 import TyCon
 import Class
@@ -462,7 +461,9 @@ pprKind = pprType
 pprParendKind = pprParendType
 
 ppr_type :: Prec -> Type -> SDoc
-ppr_type _ (TyVarTy tv)       = ppr tv
+ppr_type _ (TyVarTy tv)                -- Note [Infix type variables]
+  | isSymOcc (getOccName tv)  = parens (ppr tv)
+  | otherwise                = ppr tv
 ppr_type _ (PredTy pred)      = ifPprDebug (ptext (sLit "<pred>")) <> (ppr pred)
 ppr_type p (TyConApp tc tys)  = ppr_tc_app p tc tys
 
@@ -553,3 +554,24 @@ pprTvBndr tv | isLiftedTypeKind kind = ppr tv
               kind = tyVarKind tv
 \end{code}
 
+Note [Infix type variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In Haskell 98 you can say
+
+   f :: (a ~> b) -> b
+
+and the (~>) is considered a type variable.  However, the type
+pretty-printer in this module will just see (a ~> b) as
+
+   App (App (TyVarTy "~>") (TyVarTy "a")) (TyVarTy "b")
+
+So it'll print the type in prefix form.  To avoid confusion we must
+remember to parenthesise the operator, thus
+
+   (~>) a b -> b
+
+See Trac #2766.
+
+
+
+