Migrate cvs diff from fptools-assoc branch

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

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index fa129d3..11ec9d9 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -24,7 +24,7 @@ module TcMType (
 
   --------------------------------
   -- Instantiation
-  tcInstTyVar, tcInstType, tcInstTyVars, tcInstBoxy, tcInstBoxyTyVar,
+  tcInstTyVar, tcInstType, tcInstTyVars, tcInstBoxyTyVar,
   tcInstSigTyVars, zonkSigTyVar,
   tcInstSkolTyVar, tcInstSkolTyVars, tcInstSkolType, 
   tcSkolSigType, tcSkolSigTyVars,
@@ -58,8 +58,7 @@ import TypeRep                ( Type(..), PredType(..),  -- Friend; can see representation
 import TcType          ( TcType, TcThetaType, TcTauType, TcPredType,
                          TcTyVarSet, TcKind, TcTyVar, TcTyVarDetails(..), 
                          MetaDetails(..), SkolemInfo(..), BoxInfo(..), 
-                         BoxyTyVar, BoxyType, BoxyThetaType, BoxySigmaType, 
-                         UserTypeCtxt(..),
+                         BoxyTyVar, BoxyType, UserTypeCtxt(..),
                          isMetaTyVar, isSigTyVar, metaTvRef,
                          tcCmpPred, isClassPred, tcGetTyVar,
                          tcSplitPhiTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe, 
@@ -201,9 +200,13 @@ newMetaTyVar box_info kind
        ; ref <- newMutVar Flexi ;
        ; let name = mkSysTvName uniq fs 
              fs = case box_info of
-                       BoxTv   -> FSLIT("bx")
+                       BoxTv   -> FSLIT("t")
                        TauTv   -> FSLIT("t")
                        SigTv _ -> FSLIT("a")
+               -- We give BoxTv and TauTv the same string, because
+               -- otherwise we get user-visible differences in error
+               -- messages, which are confusing.  If you want to see
+               -- the box_info of each tyvar, use -dppr-debug
        ; return (mkTcTyVar name kind (MetaTv box_info ref)) }
 
 instMetaTyVar :: BoxInfo -> TyVar -> TcM TcTyVar
@@ -327,12 +330,6 @@ readFilledBox box_tv = ASSERT( isBoxyTyVar box_tv )
 tcInstBoxyTyVar :: TyVar -> TcM BoxyTyVar
 -- Instantiate with a BOXY type variable
 tcInstBoxyTyVar tyvar = instMetaTyVar BoxTv tyvar
-
-tcInstBoxy :: TcType -> TcM ([BoxyTyVar], BoxyThetaType, BoxySigmaType)
--- tcInstType instantiates the outer-level for-alls of a TcType with
--- fresh BOXY type variables, splits off the dictionary part, 
--- and returns the pieces.
-tcInstBoxy ty = tcInstType (mapM tcInstBoxyTyVar) ty
 \end{code}
 
 
@@ -731,14 +728,16 @@ check_poly_type (Rank 0) ubx_tup ty
   = check_tau_type (Rank 0) ubx_tup ty
 
 check_poly_type rank ubx_tup ty 
-  = let
-       (tvs, theta, tau) = tcSplitSigmaTy ty
-    in
-    check_valid_theta SigmaCtxt theta          `thenM_`
-    check_tau_type (decRank rank) ubx_tup tau  `thenM_`
-    checkFreeness tvs theta                    `thenM_`
-    checkAmbiguity tvs theta (tyVarsOfType tau)
-
+  | null tvs && null theta
+  = check_tau_type rank ubx_tup ty
+  | otherwise
+  = do { check_valid_theta SigmaCtxt theta
+       ; check_poly_type rank ubx_tup tau      -- Allow foralls to right of arrow
+       ; checkFreeness tvs theta
+       ; checkAmbiguity tvs theta (tyVarsOfType tau) }
+  where
+    (tvs, theta, tau) = tcSplitSigmaTy ty
+   
 ----------------------------------------
 check_arg_type :: Type -> TcM ()
 -- The sort of type that can instantiate a type variable,
@@ -781,8 +780,8 @@ check_tau_type rank ubx_tup (PredTy sty) = getDOpts         `thenM` \ dflags ->
 
 check_tau_type rank ubx_tup (TyVarTy _)       = returnM ()
 check_tau_type rank ubx_tup ty@(FunTy arg_ty res_ty)
-  = check_poly_type rank UT_NotOk arg_ty       `thenM_`
-    check_poly_type rank UT_Ok    res_ty
+  = check_poly_type (decRank rank) UT_NotOk arg_ty     `thenM_`
+    check_poly_type rank          UT_Ok    res_ty
 
 check_tau_type rank ubx_tup (AppTy ty1 ty2)
   = check_arg_type ty1 `thenM_` check_arg_type ty2