From: simonpj@microsoft.com <unknown>
Date: Tue, 25 Nov 2008 11:05:40 +0000 (+0000)
Subject: Fix Trac #2799: TcType.isOverloadedTy
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=524207589f410be34a7eec942e112739eb1519f8

Fix Trac #2799: TcType.isOverloadedTy

A missing case (for equality predicates) in isOverloadedTy make
bindInstsOfLocalFuns/Pats do the wrong thing.  Core Lint nailed it.

Merge to 6.10 branch.
---

diff --git a/compiler/typecheck/TcType.lhs b/compiler/typecheck/TcType.lhs
index fe5ea39..e0e7649 100644
--- a/compiler/typecheck/TcType.lhs
+++ b/compiler/typecheck/TcType.lhs
@@ -965,10 +965,13 @@ isSigmaTy (FunTy a _)    = isPredTy a
 isSigmaTy _              = False
 
 isOverloadedTy :: Type -> Bool
+-- Yes for a type of a function that might require evidence-passing
+-- Used only by bindInstsOfLocalFuns/Pats
+-- NB: be sure to check for type with an equality predicate; hence isCoVar
 isOverloadedTy ty | Just ty' <- tcView ty = isOverloadedTy ty'
-isOverloadedTy (ForAllTy _ ty) = isOverloadedTy ty
-isOverloadedTy (FunTy a _)     = isPredTy a
-isOverloadedTy _               = False
+isOverloadedTy (ForAllTy tv ty) = isCoVar tv || isOverloadedTy ty
+isOverloadedTy (FunTy a _)      = isPredTy a
+isOverloadedTy _                = False
 
 isPredTy :: Type -> Bool	-- Belongs in TcType because it does 
 				-- not look through newtypes, or predtypes (of course)