From: simonmar@microsoft.com <unknown>
Date: Thu, 28 Jun 2007 08:11:05 +0000 (+0000)
Subject: Fix typechecking bug with implicit parameters (Trac #1445)
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=52dead8037b16f86a60b4af234d1cf86dba9cee2

Fix typechecking bug with implicit parameters (Trac #1445)

tcSplitFunTy_maybe wasn't dealing with types like
	(?x::Bool) => Int
Here, tcSplitFunTy_maybe should fail (as it would if there
was a for-all), because the type is a quantified type.

See Trac #1445, and test tc230.
---

diff --git a/compiler/typecheck/TcType.lhs b/compiler/typecheck/TcType.lhs
index 5928630..01796c3 100644
--- a/compiler/typecheck/TcType.lhs
+++ b/compiler/typecheck/TcType.lhs
@@ -715,9 +715,16 @@ tcSplitFunTys ty = case tcSplitFunTy_maybe ty of
 					  (args,res') = tcSplitFunTys res
 
 tcSplitFunTy_maybe :: Type -> Maybe (Type, Type)
-tcSplitFunTy_maybe ty | Just ty' <- tcView ty = tcSplitFunTy_maybe ty'
-tcSplitFunTy_maybe (FunTy arg res)  = Just (arg, res)
-tcSplitFunTy_maybe other	    = Nothing
+tcSplitFunTy_maybe ty | Just ty' <- tcView ty           = tcSplitFunTy_maybe ty'
+tcSplitFunTy_maybe (FunTy arg res) | not (isPredTy arg) = Just (arg, res)
+tcSplitFunTy_maybe other	  			= Nothing
+	-- Note the (not (isPredTy arg)) guard
+	-- Consider	(?x::Int) => Bool
+	-- We don't want to treat this as a function type!
+	-- A concrete example is test tc230:
+	--	f :: () -> (?p :: ()) => () -> ()
+	--
+	--	g = f () ()
 
 tcSplitFunTysN
 	:: TcRhoType