From 2476a85973ed0d32021ac662486cebd0549059b8 Mon Sep 17 00:00:00 2001
From: simonpj <unknown>
Date: Tue, 9 Feb 1999 08:53:05 +0000
Subject: [PATCH] [project @ 1999-02-09 08:53:05 by simonpj] Fix typechecker
bug so that
main :: a
main = error "Urk"
gives a sensible error message rather than crashing the compiler
---
ghc/compiler/typecheck/TcBinds.lhs | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/ghc/compiler/typecheck/TcBinds.lhs b/ghc/compiler/typecheck/TcBinds.lhs
index 6f62328f3861..49dfed223b5d 100644
--- a/ghc/compiler/typecheck/TcBinds.lhs
+++ b/ghc/compiler/typecheck/TcBinds.lhs
@@ -692,17 +692,24 @@ now (ToDo).
\begin{code}
checkSigMatch top_lvl binder_names mono_ids sigs
| main_bound_here
- = mapTc check_one_sig sigs `thenTc_`
- mapTc check_main_ctxt sigs `thenTc_`
-
- -- Now unify the main_id with IO t, for any old t
+ = -- First unify the main_id with IO t, for any old t
tcSetErrCtxt mainTyCheckCtxt (
tcLookupTyCon ioTyCon_NAME `thenTc` \ ioTyCon ->
newTyVarTy boxedTypeKind `thenNF_Tc` \ t_tv ->
unifyTauTy ((mkTyConApp ioTyCon [t_tv]))
(idType main_mono_id)
) `thenTc_`
- returnTc (Just ([], emptyLIE))
+
+ -- Now check the signatures
+ -- Must do this after the unification with IO t,
+ -- in case of a silly signature like
+ -- main :: forall a. a
+ -- The unification to IO t will bind the type variable 'a',
+ -- which is just waht check_one_sig looks for
+ mapTc check_one_sig sigs `thenTc_`
+ mapTc check_main_ctxt sigs `thenTc_`
+
+ returnTc (Just ([], emptyLIE))
| not (null sigs)
= mapTc check_one_sig sigs `thenTc_`
--
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