EqPred pretty prints as ~ and equalities without brackets

[ghc-hetmet.git] / compiler / parser / Parser.y.pp

diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp
index 009eddc..f72c8b9 100644 (file)
--- a/compiler/parser/Parser.y.pp
+++ b/compiler/parser/Parser.y.pp
@@ -971,8 +971,13 @@ ctype      :: { LHsType RdrName }
 -- errors in ctype.  The basic problem is that
 --     (Eq a, Ord a)
 -- looks so much like a tuple type.  We can't tell until we find the =>
+--
+-- We have the t1 ~ t2 form here and in gentype, to permit an individual
+-- equational constraint without parenthesis.
 context :: { LHsContext RdrName }
-       : btype                         {% checkContext $1 }
+        : btype '~'      btype         {% checkContext
+                                            (LL $ HsPredTy (HsEqualP $1 $3)) }
+       | btype                         {% checkContext $1 }
 
 type :: { LHsType RdrName }
        : ipvar '::' gentype            { LL (HsPredTy (HsIParam (unLoc $1) $3)) }
@@ -983,7 +988,7 @@ gentype :: { LHsType RdrName }
         | btype qtyconop gentype        { LL $ HsOpTy $1 $2 $3 }
         | btype tyvarop  gentype       { LL $ HsOpTy $1 $2 $3 }
        | btype '->'     ctype          { LL $ HsFunTy $1 $3 }
-        | btype '~'      gentype       { LL $ HsPredTy (HsEqualP $1 $3) }
+        | btype '~'      btype         { LL $ HsPredTy (HsEqualP $1 $3) }
 
 btype :: { LHsType RdrName }
        : btype atype                   { LL $ HsAppTy $1 $2 }