Result type signatures are no longer supported (partial)

I had failed to remove the bit where result type signatures bind
lexical type variables.  And now we are planning to remove them entirely.

This commit therefore does a partial removal (to avoid destablising 6.6).
It also arranges that
	f :: sig = rhs
means a *pattern* binding (not a function binding with no arguments
and a result signature), which makes sense.

diff --git a/compiler/hsSyn/HsBinds.lhs b/compiler/hsSyn/HsBinds.lhs
index 78a2234..31c1cae 100644 (file)
--- a/compiler/hsSyn/HsBinds.lhs
+++ b/compiler/hsSyn/HsBinds.lhs
@@ -59,14 +59,15 @@ type LHsBind  id  = Located (HsBind id)
 data HsBind id
   = FunBind {  -- FunBind is used for both functions   f x = e
                -- and variables                        f = \x -> e
--- Reason 1: the Match stuff lets us have an optional
---        result type sig      f :: a->a = ...mentions a...
+-- Reason 1: Special case for type inference: see TcBinds.tcMonoBinds
 --
--- Reason 2: Special case for type inference: see TcBinds.tcMonoBinds
---
--- Reason 3: instance decls can only have FunBinds, which is convenient
+-- Reason 2: instance decls can only have FunBinds, which is convenient
 --          If you change this, you'll need tochange e.g. rnMethodBinds
 
+-- But note that the form      f :: a->a = ...
+-- parses as a pattern binding, just like
+--                     (f :: a -> a) = ... 
+
        fun_id :: Located id,
 
        fun_infix :: Bool,      -- True => infix declaration

diff --git a/compiler/parser/RdrHsSyn.lhs b/compiler/parser/RdrHsSyn.lhs
index 2e846a5..ca24070 100644 (file)
--- a/compiler/parser/RdrHsSyn.lhs
+++ b/compiler/parser/RdrHsSyn.lhs
@@ -596,6 +596,10 @@ checkValDef :: LHsExpr RdrName
            -> Located (GRHSs RdrName)
            -> P (HsBind RdrName)
 
+checkValDef lhs (Just sig) grhss
+       -- x :: ty = rhs  parses as a *pattern* binding
+  = checkPatBind (L (combineLocs lhs sig) (ExprWithTySig lhs sig)) grhss
+
 checkValDef lhs opt_sig grhss
   = do { mb_fun <- isFunLhs lhs
        ; case mb_fun of

diff --git a/compiler/typecheck/TcMatches.lhs b/compiler/typecheck/TcMatches.lhs
index 07a1094..27d1e9b 100644 (file)
--- a/compiler/typecheck/TcMatches.lhs
+++ b/compiler/typecheck/TcMatches.lhs
@@ -23,10 +23,8 @@ import HsSyn         ( HsExpr(..), LHsExpr, MatchGroup(..),
                          ExprCoFn )
 
 import TcRnMonad
-import TcHsType                ( tcPatSig, UserTypeCtxt(..) )
 import Inst            ( newMethodFromName )
-import TcEnv           ( TcId, tcLookupLocalIds, tcLookupId, tcExtendIdEnv, 
-                         tcExtendTyVarEnv2 )
+import TcEnv           ( TcId, tcLookupLocalIds, tcLookupId, tcExtendIdEnv )
 import TcPat           ( PatCtxt(..), tcPats, tcPat )
 import TcMType         ( newFlexiTyVarTy, newFlexiTyVarTys ) 
 import TcType          ( TcType, TcRhoType, 
@@ -165,15 +163,16 @@ tcMatch ctxt pat_tys rhs_ty match
       = addErrCtxt (matchCtxt (mc_what ctxt) match)    $       
         do { (pats', grhss') <- tcPats LamPat pats pat_tys rhs_ty $
                                tc_grhss ctxt maybe_rhs_sig grhss
-          ; returnM (Match pats' Nothing grhss') }
+          ; return (Match pats' Nothing grhss') }
 
     tc_grhss ctxt Nothing grhss rhs_ty 
       = tcGRHSs ctxt grhss rhs_ty      -- No result signature
 
+       -- Result type sigs are no longer supported
     tc_grhss ctxt (Just res_sig) grhss rhs_ty 
-      = do { (inner_ty, sig_tvs) <- tcPatSig ResSigCtxt res_sig rhs_ty
-          ; tcExtendTyVarEnv2 sig_tvs $
-            tcGRHSs ctxt grhss inner_ty }
+      = do { addErr (ptext SLIT("Ignoring (deprecated) result type signature")
+                       <+> ppr res_sig)
+          ; tcGRHSs ctxt grhss rhs_ty }
 
 -------------
 tcGRHSs :: TcMatchCtxt -> GRHSs Name -> BoxyRhoType -> TcM (GRHSs TcId)
@@ -500,6 +499,7 @@ checkArgs fun (MatchGroup (match1:matches) _)
 
     args_in_match :: LMatch Name -> Int
     args_in_match (L _ (Match pats _ _)) = length pats
+checkArgs fun other = panic "TcPat.checkArgs"  -- Matches always non-empty
 \end{code}
 
 \begin{code}