[project @ 2001-03-19 16:15:29 by simonpj]

Reorder the calls to
	tcSimplifyTop
and
	tcCheckMain

in TcModule.  We must to tcCheckMain first, else we get a bogus
complaint when compiling

	main = return ()

(Something about ambiguous monad.)

diff --git a/ghc/compiler/typecheck/TcModule.lhs b/ghc/compiler/typecheck/TcModule.lhs
index e6b03a1..f6c9f64 100644 (file)
--- a/ghc/compiler/typecheck/TcModule.lhs
+++ b/ghc/compiler/typecheck/TcModule.lhs
@@ -368,12 +368,24 @@ tcModule pcs hst get_fixity this_mod decls
        tcForeignExports decls                  `thenTc`    \ (lie_fodecls,   foe_binds, foe_decls) ->
        tcSourceRules source_rules              `thenNF_Tc` \ (lie_rules,     more_local_rules) ->
        
+               -- CHECK THAT main IS DEFINED WITH RIGHT TYPE, IF REQUIRED
+        traceTc (text "Tc6")                   `thenNF_Tc_`
+       tcCheckMain this_mod                    `thenTc_`
+
             -- Deal with constant or ambiguous InstIds.  How could
             -- there be ambiguous ones?  They can only arise if a
             -- top-level decl falls under the monomorphism
             -- restriction, and no subsequent decl instantiates its
             -- type.  (Usually, ambiguous type variables are resolved
             -- during the generalisation step.)
+            --
+            -- Note that we must do this *after* tcCheckMain, because of the
+            -- following bizarre case: 
+            --         main = return ()
+            -- Here, we infer main :: forall a. m a, where m is a free
+            -- type variable.  tcCheckMain will unify it with IO, and that
+            -- must happen before tcSimplifyTop, since the latter will report
+            -- m as ambiguous
        let
            lie_alldecls = lie_valdecls  `plusLIE`
                           lie_instdecls `plusLIE`
@@ -381,11 +393,7 @@ tcModule pcs hst get_fixity this_mod decls
                           lie_fodecls   `plusLIE`
                           lie_rules
        in
-        traceTc (text "Tc6")                           `thenNF_Tc_`
-       tcSimplifyTop lie_alldecls                      `thenTc` \ const_inst_binds ->
-       
-               -- CHECK THAT main IS DEFINED WITH RIGHT TYPE, IF REQUIRED
-       tcCheckMain this_mod            `thenTc_`
+       tcSimplifyTop lie_alldecls      `thenTc` \ const_inst_binds ->
        
            -- Backsubstitution.    This must be done last.
            -- Even tcSimplifyTop may do some unification.
@@ -482,7 +490,8 @@ typecheckIface dflags pcs hst mod_iface (syn_map, decls)
 
              mod_details = ModDetails { md_types = mkTypeEnv local_things,
                                         md_insts = map iDFunId local_inst_info,
-                                        md_rules = [(id,rule) | IfaceRuleOut id rule <- local_rules] }
+                                        md_rules = [(id,rule) | IfaceRuleOut id rule <- local_rules],
+                                        md_binds = [] }
                        -- All the rules from an interface are of the IfaceRuleOut form
          in
           returnTc (new_pcs, mod_details)
@@ -676,7 +685,7 @@ printIfaceDump dflags (Just (_, details))
 dump_tc_iface results
   = vcat [pprModDetails (ModDetails {md_types = tc_env results, 
                                     md_insts = tc_insts results,
-                                    md_rules = []}) ,
+                                    md_rules = [], md_binds = []}) ,
          ppr_rules (tc_rules results),
 
          ppr_gen_tycons [tc | ATyCon tc <- nameEnvElts (tc_env results)]