[project @ 2002-03-12 09:12:57 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index aaed7c2..6067ea8 100644 (file)
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -4,7 +4,7 @@
 \section[TcDefaults]{Typechecking \tr{default} declarations}
 
 \begin{code}
-module TcDefaults ( tcDefaults ) where
+module TcDefaults ( tcDefaults, defaultDefaultTys ) where
 
 #include "HsVersions.h"
 
@@ -12,60 +12,63 @@ import HsSyn                ( HsDecl(..), DefaultDecl(..) )
 import RnHsSyn         ( RenamedHsDecl )
 
 import TcMonad
-import TcEnv           ( tcLookupClassByKey_maybe )
+import TcEnv           ( tcLookupGlobal_maybe )
 import TcMonoType      ( tcHsType )
-import TcSimplify      ( tcSimplifyCheckThetas )
+import TcSimplify      ( tcSimplifyDefault )
 
 import TysWiredIn      ( integerTy, doubleTy )
-import Type             ( Type )
-import Unique          ( numClassKey )
+import TcType           ( Type, mkClassPred, isTauTy )
+import PrelNames       ( numClassName )
 import Outputable
+import HscTypes                ( TyThing(..) )
 \end{code}
 
 \begin{code}
-default_default = [integerTy, doubleTy]
+defaultDefaultTys = [integerTy, doubleTy]
 
 tcDefaults :: [RenamedHsDecl]
-          -> TcM s [Type]          -- defaulting types to heave
+          -> TcM [Type]            -- defaulting types to heave
                                    -- into Tc monad for later use
                                    -- in Disambig.
 tcDefaults decls = tc_defaults [default_decl | DefD default_decl <- decls]
 
-tc_defaults [] = returnTc default_default
+tc_defaults [] = returnTc defaultDefaultTys
 
 tc_defaults [DefaultDecl [] locn]
   = returnTc []                -- no defaults
 
 tc_defaults [DefaultDecl mono_tys locn]
-  = tcLookupClassByKey_maybe numClassKey       `thenNF_Tc` \ maybe_num ->
-    case maybe_num of {
-       Nothing ->      -- Num has not been sucked in, so the defaults will
-                       -- never be used; so simply discard the default decl.
-                       -- This slightly benefits modules that don't use any
-                       -- numeric stuff at all, by avoid the necessity of
-                       -- always sucking in Num
-               returnTc [] ;
-
-       Just num ->     -- The common case
-
-    tcAddSrcLoc locn $
-    mapTc tcHsType mono_tys    `thenTc` \ tau_tys ->
-
-           -- Check that all the types are instances of Num
-           -- We only care about whether it worked or not
-    tcAddErrCtxt defaultDeclCtxt               $
-    tcSimplifyCheckThetas
-               [{- Nothing given -}]
-               [ (num, [ty]) | ty <- tau_tys ] `thenTc_`
-
-    returnTc tau_tys
-    }
+  = tcLookupGlobal_maybe numClassName  `thenNF_Tc` \ maybe_num ->
+    case maybe_num of
+       Just (AClass num_class) -> common_case num_class
+       other                   -> returnTc []
+               -- In the Nothing case, Num has not been sucked in, so the 
+               -- defaults will never be used; so simply discard the default decl.
+               -- This slightly benefits modules that don't use any
+               -- numeric stuff at all, by avoid the necessity of
+               -- always sucking in Num
+  where
+    common_case num_class
+      = tcAddSrcLoc locn               $
+       tcAddErrCtxt defaultDeclCtxt    $
+       mapTc tc_default_ty mono_tys    `thenTc` \ tau_tys ->
+    
+               -- Check that all the types are instances of Num
+               -- We only care about whether it worked or not
+       tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys]  `thenTc_`
+    
+       returnTc tau_tys
 
 tc_defaults decls@(DefaultDecl _ loc : _) =
     tcAddSrcLoc loc $
     failWithTc (dupDefaultDeclErr decls)
 
 
+tc_default_ty hs_ty 
+ = tcHsType hs_ty                              `thenTc` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)     `thenTc_`
+   returnTc ty
+
 defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
                    $$ ptext SLIT("is an instance of class Num")
 
@@ -75,5 +78,8 @@ dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things)
       4  (vcat (map pp dup_things))
   where
     pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
+
+polyDefErr ty 
+  = hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty) 
 \end{code}