Fix a bug in the handling of implication constraints (Trac #1430)

[ghc-hetmet.git] / compiler / typecheck / TcPat.lhs

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index e7fd6ca..5384e4a 100644 (file)
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -228,7 +228,7 @@ unBoxArgType ty pp_this
 
 Note [Nesting]
 ~~~~~~~~~~~~~~
-tcPat takes a "thing inside" over which the patter scopes.  This is partly
+tcPat takes a "thing inside" over which the pattern scopes.  This is partly
 so that tcPat can extend the environment for the thing_inside, but also 
 so that constraints arising in the thing_inside can be discharged by the
 pattern.
@@ -546,7 +546,7 @@ tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
         -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
         -> TcM (Pat TcId, [TcTyVar], a)
 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
-  = do { let (univ_tvs, ex_tvs, eq_spec, theta, arg_tys) = dataConFullSig data_con
+  = do { let (univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _) = dataConFullSig data_con
              skol_info = PatSkol data_con
              origin    = SigOrigin skol_info
 
@@ -583,9 +583,8 @@ tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
             ex_tvs' ++ inner_tvs, res)
        }
   where
-    -- Split against the family tycon if the pattern constructor belongs to a
-    -- representation tycon.
-    --
+    -- Split against the family tycon if the pattern constructor 
+    -- belongs to a family instance tycon.
     boxySplitTyConAppWithFamily tycon pat_ty =
       traceTc traceMsg >>
       case tyConFamInst_maybe tycon of
@@ -813,6 +812,19 @@ tcOverloadedLit orig lit@(HsFractional r fr) res_ty
   = do         { expr <- newLitInst orig lit res_ty
        ; return (HsFractional r expr) }
 
+tcOverloadedLit orig lit@(HsIsString s fr) res_ty
+  | not (fr `isHsVar` fromStringName)  -- c.f. HsIntegral case
+  = do { str_ty <- tcMetaTy stringTyConName
+       ; fr' <- tcSyntaxOp orig fr (mkFunTy str_ty res_ty)
+       ; return (HsIsString s (HsApp (noLoc fr') (nlHsLit (HsString s)))) }
+
+  | Just expr <- shortCutStringLit s res_ty 
+  = return (HsIsString s expr)
+
+  | otherwise
+  = do         { expr <- newLitInst orig lit res_ty
+       ; return (HsIsString s expr) }
+
 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
 newLitInst orig lit res_ty     -- Make a LitInst
   = do         { loc <- getInstLoc orig
@@ -943,7 +955,7 @@ badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
 
 lazyPatErr pat tvs
   = failWithTc $
-    hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
+    hang (ptext SLIT("A lazy (~) pattern cannot bind existential type variables"))
        2 (vcat (map pprSkolTvBinding tvs))
 
 nonRigidMatch con