[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 b9b74c3..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"
 
@@ -14,17 +14,17 @@ import RnHsSyn              ( RenamedHsDecl )
 import TcMonad
 import TcEnv           ( tcLookupGlobal_maybe )
 import TcMonoType      ( tcHsType )
-import TcSimplify      ( tcSimplifyCheckThetas )
+import TcSimplify      ( tcSimplifyDefault )
 
 import TysWiredIn      ( integerTy, doubleTy )
-import Type             ( Type )
+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 [Type]            -- defaulting types to heave
@@ -32,7 +32,7 @@ tcDefaults :: [RenamedHsDecl]
                                    -- 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
@@ -49,24 +49,26 @@ tc_defaults [DefaultDecl mono_tys locn]
                -- always sucking in Num
   where
     common_case num_class
-      = tcAddSrcLoc locn $
-       mapTc tcHsType mono_tys `thenTc` \ tau_tys ->
+      = 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
-       tcAddErrCtxt defaultDeclCtxt            $
-       tcSimplifyCheckThetas
-                   [{- Nothing given -}]
-                   [ (num_class, [ty]) | ty <- tau_tys ]       `thenTc_`
+       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")
 
@@ -76,5 +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}