X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDefaults.lhs;h=50b5767cef93614c00d88330f39d0e26931392bb;hp=0011215fe6e1fbc9b0fbd41d9854df635aff6172;hb=HEAD;hpb=49c98d143c382a1341e1046f5ca00819a25691ba

diff --git a/compiler/typecheck/TcDefaults.lhs b/compiler/typecheck/TcDefaults.lhs
index 0011215..50b5767 100644
--- a/compiler/typecheck/TcDefaults.lhs
+++ b/compiler/typecheck/TcDefaults.lhs
@@ -7,18 +7,20 @@
 \begin{code}
 module TcDefaults ( tcDefaults ) where
 
-#include "HsVersions.h"
-
 import HsSyn
 import Name
+import Class
 import TcRnMonad
 import TcEnv
 import TcHsType
 import TcSimplify
 import TcType
 import PrelNames
+import DynFlags
 import SrcLoc
+import Data.Maybe
 import Outputable
+import FastString
 \end{code}
 
 \begin{code}
@@ -28,7 +30,7 @@ tcDefaults :: [LDefaultDecl Name]
 				    -- in Disambig.
 
 tcDefaults [] 
-  = getDefaultTys		-- No default declaration, so get the
+  = getDeclaredDefaultTys	-- No default declaration, so get the
 				-- default types from the envt; 
 				-- i.e. use the curent ones
 				-- (the caller will put them back there)
@@ -39,42 +41,62 @@ tcDefaults []
 	-- one group, only for the next group to ignore them and install
 	-- defaultDefaultTys
 
-tcDefaults [L locn (DefaultDecl [])]
-  = returnM (Just [])		-- Default declaration specifying no types
+tcDefaults [L _ (DefaultDecl [])]
+  = return (Just [])		-- Default declaration specifying no types
 
 tcDefaults [L locn (DefaultDecl mono_tys)]
   = setSrcSpan locn 			$
     addErrCtxt defaultDeclCtxt		$
-    tcLookupClass numClassName		`thenM` \ num_class ->
-    mappM tc_default_ty mono_tys	`thenM` \ 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]	`thenM_`
+    do	{ ovl_str <- xoptM Opt_OverloadedStrings
+	; num_class    <- tcLookupClass numClassName
+	; is_str_class <- tcLookupClass isStringClassName
+	; let deflt_clss | ovl_str   = [num_class, is_str_class]
+			 | otherwise = [num_class]
+
+	; tau_tys <- mapM (tc_default_ty deflt_clss) mono_tys
     
-    returnM (Just tau_tys)
+	; return (Just tau_tys) }
 
-tcDefaults decls@(L locn (DefaultDecl _) : _) =
-    setSrcSpan locn $
+tcDefaults decls@(L locn (DefaultDecl _) : _)
+  = setSrcSpan locn $
     failWithTc (dupDefaultDeclErr decls)
 
 
-tc_default_ty hs_ty 
- = tcHsSigType DefaultDeclCtxt hs_ty		`thenM` \ ty ->
-   checkTc (isTauTy ty) (polyDefErr hs_ty)	`thenM_`
-   returnM ty
+tc_default_ty :: [Class] -> LHsType Name -> TcM Type
+tc_default_ty deflt_clss hs_ty 
+ = do	{ ty <- tcHsSigType DefaultDeclCtxt hs_ty
+	; checkTc (isTauTy ty) (polyDefErr hs_ty)
 
-defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
-		    $$ ptext SLIT("is an instance of class Num")
+	-- Check that the type is an instance of at least one of the deflt_clss
+	; oks <- mapM (check_instance ty) deflt_clss
+	; checkTc (or oks) (badDefaultTy ty deflt_clss)
+	; return ty }
 
+check_instance :: Type -> Class -> TcM Bool
+  -- Check that ty is an instance of cls
+  -- We only care about whether it worked or not; return a boolean
+check_instance ty cls
+  = do	{ (_, mb_res) <- tryTc (simplifyDefault [mkClassPred cls [ty]])
+	; return (isJust mb_res) }
+    
+defaultDeclCtxt :: SDoc
+defaultDeclCtxt = ptext (sLit "When checking the types in a default declaration")
 
+dupDefaultDeclErr :: [Located (DefaultDecl Name)] -> SDoc
 dupDefaultDeclErr (L _ (DefaultDecl _) : dup_things)
-  = hang (ptext SLIT("Multiple default declarations"))
-      4  (vcat (map pp dup_things))
+  = hang (ptext (sLit "Multiple default declarations"))
+       2 (vcat (map pp dup_things))
   where
-    pp (L locn (DefaultDecl _)) = ptext SLIT("here was another default declaration") <+> ppr locn
+    pp (L locn (DefaultDecl _)) = ptext (sLit "here was another default declaration") <+> ppr locn
+dupDefaultDeclErr [] = panic "dupDefaultDeclErr []"
 
+polyDefErr :: LHsType Name -> SDoc
 polyDefErr ty 
-  = hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty) 
+  = hang (ptext (sLit "Illegal polymorphic type in default declaration") <> colon) 2 (ppr ty) 
+
+badDefaultTy :: Type -> [Class] -> SDoc
+badDefaultTy ty deflt_clss
+  = hang (ptext (sLit "The default type") <+> quotes (ppr ty) <+> ptext (sLit "is not an instance of"))
+       2 (foldr1 (\a b -> a <+> ptext (sLit "or") <+> b) (map (quotes. ppr) deflt_clss))
 \end{code}