Comments, and remove export of checkAmbiguity

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

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index 1ae1b2b..3437549 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -47,7 +47,7 @@ module TcMType (
   -- Checking type validity
   Rank, UserTypeCtxt(..), checkValidType, 
   SourceTyCtxt(..), checkValidTheta, checkFreeness,
-  checkValidInstHead, checkValidInstance, checkAmbiguity,
+  checkValidInstHead, checkValidInstance, 
   checkInstTermination, checkValidTypeInst, checkTyFamFreeness,
   validDerivPred, arityErr, 
 
@@ -1030,6 +1030,7 @@ If the list of tv_names is empty, we have a monotype, and then we
 don't need to check for ambiguity either, because the test can't fail
 (see is_ambig).
 
+
 \begin{code}
 checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM ()
 checkAmbiguity forall_tyvars theta tau_tyvars
@@ -1038,11 +1039,7 @@ checkAmbiguity forall_tyvars theta tau_tyvars
     complain pred     = addErrTc (ambigErr pred)
     extended_tau_vars = grow theta tau_tyvars
 
-       -- Only a *class* predicate can give rise to ambiguity
-       -- An *implicit parameter* cannot.  For example:
-       --      foo :: (?x :: [a]) => Int
-       --      foo = length ?x
-       -- is fine.  The call site will suppply a particular 'x'
+       -- See Note [Implicit parameters and ambiguity] in TcSimplify
     is_ambig pred     = isClassPred  pred &&
                        any ambig_var (varSetElems (tyVarsOfPred pred))
 
@@ -1442,16 +1439,4 @@ sizePred :: PredType -> Int
 sizePred (ClassP _ tys')   = sizeTypes tys'
 sizePred (IParam _ ty)     = sizeType ty
 sizePred (EqPred ty1 ty2)  = sizeType ty1 + sizeType ty2
-
--- Type family instances occuring in a type after expanding synonyms
-tyFamInsts :: Type -> [(TyCon, [Type])]
-tyFamInsts ty 
-  | Just exp_ty <- tcView ty    = tyFamInsts exp_ty
-tyFamInsts (TyVarTy _)          = []
-tyFamInsts (TyConApp tc tys) 
-  | isOpenSynTyCon tc           = [(tc, tys)]
-  | otherwise                   = concat (map tyFamInsts tys)
-tyFamInsts (FunTy ty1 ty2)      = tyFamInsts ty1 ++ tyFamInsts ty2
-tyFamInsts (AppTy ty1 ty2)      = tyFamInsts ty1 ++ tyFamInsts ty2
-tyFamInsts (ForAllTy _ ty)      = tyFamInsts ty
 \end{code}