[project @ 2001-11-26 09:20:25 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcMatches.lhs b/ghc/compiler/typecheck/TcMatches.lhs
index 31cfa28..fbc20af 100644 (file)
--- a/ghc/compiler/typecheck/TcMatches.lhs
+++ b/ghc/compiler/typecheck/TcMatches.lhs
@@ -21,14 +21,15 @@ import RnHsSyn              ( RenamedMatch, RenamedGRHSs, RenamedStmt, RenamedPat, RenamedMa
 import TcHsSyn         ( TcMatch, TcGRHSs, TcStmt, TcDictBinds, TypecheckedPat )
 
 import TcMonad
-import TcMonoType      ( tcAddScopedTyVars, checkSigTyVars, tcHsSigType, UserTypeCtxt(..), sigPatCtxt )
+import TcMonoType      ( tcAddScopedTyVars, tcHsSigType, UserTypeCtxt(..) )
 import Inst            ( LIE, isEmptyLIE, plusLIE, emptyLIE, plusLIEs, lieToList )
 import TcEnv           ( TcId, tcLookupLocalIds, tcExtendLocalValEnv, tcExtendGlobalTyVars )
 import TcPat           ( tcPat, tcMonoPatBndr, polyPatSig )
-import TcMType         ( newTyVarTy, unifyFunTy, unifyTauTy )
+import TcMType         ( newTyVarTy )
 import TcType          ( TcType, TcTyVar, tyVarsOfType, isTauTy,  
                          mkFunTy, isOverloadedTy, liftedTypeKind, openTypeKind  )
 import TcBinds         ( tcBindsAndThen )
+import TcUnify         ( subFunTy, unifyTauTy, checkSigTyVars, sigPatCtxt )
 import TcSimplify      ( tcSimplifyCheck, bindInstsOfLocalFuns )
 import Name            ( Name )
 import TysWiredIn      ( boolTy )
@@ -77,7 +78,7 @@ tcMatchesFun xve fun_name expected_ty matches@(first_match:_)
        -- because inconsistency between branches
        -- may show up as something wrong with the (non-existent) type signature
 
-       -- No need to zonk expected_ty, because unifyFunTy does that on the fly
+       -- No need to zonk expected_ty, because subFunTy does that on the fly
     tcMatches xve (FunRhs fun_name) matches expected_ty
 \end{code}
 
@@ -280,7 +281,10 @@ tc_match_pats [] expected_ty
   = returnTc (expected_ty, [], emptyLIE, emptyBag, emptyBag, emptyLIE)
 
 tc_match_pats (pat:pats) expected_ty
-  = unifyFunTy expected_ty             `thenTc` \ (arg_ty, rest_ty) ->
+  = subFunTy expected_ty               `thenTc` \ (arg_ty, rest_ty) ->
+       -- This is the unique place we call subFunTy
+       -- The point is that if expected_y is a "hole", we want 
+       -- to make arg_ty and rest_ty as "holes" too.
     tcPat tcMonoPatBndr pat arg_ty     `thenTc` \ (pat', lie_req, pat_tvs, pat_ids, lie_avail) ->
     tc_match_pats pats rest_ty         `thenTc` \ (rhs_ty, pats', lie_reqs, pats_tvs, pats_ids, lie_avails) ->
     returnTc ( rhs_ty,