X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcDefaults.lhs;h=66e56ef74509969aefa734a3b1fada9ea1ec2a62;hb=b0604aad2c311d8713c2497afa6373bd938d501b;hp=bb0557d4b603c18a48ce171e5226fca28b8d53b0;hpb=7a3bd641457666e10d0a47be9f22762e03defbf0;p=ghc-hetmet.git

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index bb0557d..66e56ef 100644
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,76 +1,80 @@
 %
-% (c) The AQUA Project, Glasgow University, 1993-1995
+% (c) The AQUA Project, Glasgow University, 1993-1998
 %
 \section[TcDefaults]{Typechecking \tr{default} declarations}
 
 \begin{code}
-#include "HsVersions.h"
-
-module TcDefaults ( tcDefaults ) where
+module TcDefaults ( tcDefaults, defaultDefaultTys ) where
 
-IMP_Ubiq()
+#include "HsVersions.h"
 
-import HsSyn		( HsDecl(..), TyDecl, ClassDecl, InstDecl, HsBinds,
-			  DefaultDecl(..), HsType, IfaceSig,
-			  HsExpr, HsLit, ArithSeqInfo, Fake, InPat)
-import RnHsSyn		( RenamedHsDecl(..), RenamedDefaultDecl(..) )
-import TcHsSyn		( TcIdOcc )
+import HsSyn		( HsDecl(..), DefaultDecl(..) )
+import RnHsSyn		( RenamedHsDecl )
 
 import TcMonad
-import Inst		( InstOrigin(..) )
-import TcEnv		( tcLookupClassByKey )
-import SpecEnv		( SpecEnv )
+import TcEnv		( tcLookupGlobal_maybe )
 import TcMonoType	( tcHsType )
 import TcSimplify	( tcSimplifyCheckThetas )
 
-import TysWiredIn	( intTy, doubleTy, unitTy )
-import Unique		( numClassKey )
-import Pretty		( ppStr, ppAboves )
-import ErrUtils		( addShortErrLocLine )
-import Util
+import TysWiredIn	( integerTy, doubleTy )
+import TcType           ( Type, mkClassPred )
+import PrelNames	( numClassName )
+import Outputable
+import HscTypes		( TyThing(..) )
 \end{code}
 
 \begin{code}
-default_default = [intTy, doubleTy] 	    -- language-specified default `default'
+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 mono_tys locn]
-  = tcAddSrcLoc locn $
-    mapTc tcHsType mono_tys	`thenTc` \ tau_tys ->
+tc_defaults [DefaultDecl [] locn]
+  = returnTc []		-- no defaults
 
-    case tau_tys of
-      [] -> returnTc []		-- no defaults
+tc_defaults [DefaultDecl mono_tys locn]
+  = 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 $
+    	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 -}]
+ 		    [ mkClassPred num_class [ty] | ty <- tau_tys ]	`thenTc_`
+    
+    	returnTc tau_tys
 
-      _  ->
-	    -- Check that all the types are instances of Num
-	    -- We only care about whether it worked or not
 
-	tcLookupClassByKey numClassKey			`thenNF_Tc` \ num ->
-	tcSimplifyCheckThetas
-		[ (num, ty) | ty <- tau_tys ]		`thenTc_`
+tc_defaults decls@(DefaultDecl _ loc : _) =
+    tcAddSrcLoc loc $
+    failWithTc (dupDefaultDeclErr decls)
 
-	returnTc tau_tys
 
-tc_defaults decls
-  = failTc (dupDefaultDeclErr decls)
+defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
+		    $$ ptext SLIT("is an instance of class Num")
 
 
-dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things) sty
-  = ppAboves (item1 : map dup_item dup_things)
+dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things)
+  = hang (ptext SLIT("Multiple default declarations"))
+      4  (vcat (map pp dup_things))
   where
-    item1
-      = addShortErrLocLine locn1 (\ sty ->
-	ppStr "multiple default declarations") sty
-
-    dup_item (DefaultDecl _ locn)
-      = addShortErrLocLine locn (\ sty ->
-	ppStr "here was another default declaration") sty
-
+    pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
 \end{code}
+