Big tidy-up of deriving code

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

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index 0845853..e2381b6 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -62,7 +62,6 @@ module TcMType (
 import TypeRep
 import TcType
 import Type
-import Type
 import Coercion
 import Class
 import TyCon
@@ -360,7 +359,7 @@ data LookupTyVarResult      -- The result of a lookupTcTyVar call
 
 lookupTcTyVar :: TcTyVar -> TcM LookupTyVarResult
 lookupTcTyVar tyvar 
-  = ASSERT( isTcTyVar tyvar )
+  = ASSERT2( isTcTyVar tyvar, ppr tyvar )
     case details of
       SkolemTv _   -> return (DoneTv details)
       MetaTv _ ref -> do { meta_details <- readMutVar ref
@@ -925,14 +924,14 @@ check_valid_theta ctxt theta
 
 -------------------------
 check_pred_ty dflags ctxt pred@(ClassP cls tys)
-  =    -- Class predicates are valid in all contexts
-    checkTc (arity == n_tys) arity_err         `thenM_`
-
-       -- Check the form of the argument types
-    mappM_ check_arg_type tys                          `thenM_`
-    checkTc (check_class_pred_tys dflags ctxt tys)
-           (predTyVarErr pred $$ how_to_allow)
-
+  = do {       -- Class predicates are valid in all contexts
+       ; checkTc (arity == n_tys) arity_err
+
+               -- Check the form of the argument types
+       ; mappM_ check_arg_type tys
+       ; checkTc (check_class_pred_tys dflags ctxt tys)
+                (predTyVarErr pred $$ how_to_allow)
+       }
   where
     class_name = className cls
     arity      = classArity cls
@@ -940,10 +939,23 @@ check_pred_ty dflags ctxt pred@(ClassP cls tys)
     arity_err  = arityErr "Class" class_name arity n_tys
     how_to_allow = parens (ptext SLIT("Use -fglasgow-exts to permit this"))
 
+check_pred_ty dflags ctxt pred@(EqPred ty1 ty2)
+  = do {       -- Equational constraints are valid in all contexts if indexed
+               -- types are permitted
+       ; checkTc (dopt Opt_IndexedTypes dflags) (eqPredTyErr pred)
+
+               -- Check the form of the argument types
+       ; check_eq_arg_type ty1
+       ; check_eq_arg_type ty2
+       }
+  where 
+    check_eq_arg_type = check_poly_type (Rank 0) UT_NotOk
+
 check_pred_ty dflags SigmaCtxt (IParam _ ty) = check_arg_type ty
-       -- Implicit parameters only allows in type
+       -- Implicit parameters only allowed in type
        -- signatures; not in instance decls, superclasses etc
-       -- The reason for not allowing implicit params in instances is a bit subtle
+       -- The reason for not allowing implicit params in instances is a bit
+       -- subtle.
        -- If we allowed        instance (?x::Int, Eq a) => Foo [a] where ...
        -- then when we saw (e :: (?x::Int) => t) it would be unclear how to 
        -- discharge all the potential usas of the ?x in e.   For example, a
@@ -1058,6 +1070,9 @@ checkThetaCtxt ctxt theta
          ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ]
 
 badPredTyErr sty = ptext SLIT("Illegal constraint") <+> pprPred sty
+eqPredTyErr  sty = ptext SLIT("Illegal equational constraint") <+> pprPred sty
+                  $$
+                  parens (ptext SLIT("Use -findexed-types to permit this"))
 predTyVarErr pred  = sep [ptext SLIT("Non type-variable argument"),
                          nest 2 (ptext SLIT("in the constraint:") <+> pprPred pred)]
 dupPredWarn dups   = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups)
@@ -1154,7 +1169,7 @@ checkValidInstance tyvars theta clas inst_tys
        -- Check that instance inference will terminate (if we care)
        -- For Haskell 98, checkValidTheta has already done that
        ; when (gla_exts && not undecidable_ok) $
-         mapM_ failWithTc (checkInstTermination inst_tys theta)
+         mapM_ addErrTc (checkInstTermination inst_tys theta)
        
        -- The Coverage Condition
        ; checkTc (undecidable_ok || checkInstCoverage clas inst_tys)