X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcDefaults.lhs;h=a3c292b82368ab392ef43638917fcc3a37f0480c;hb=e921b2e307532e0f30eefa88b11a124be592bde4;hp=0296080e8aa8679c9d627b6677be4303c4f74213;hpb=ca5a4a480d10d61e5b7a52eb4d556e8b8c33e69d;p=ghc-hetmet.git

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index 0296080..a3c292b 100644
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,55 +1,81 @@
 %
-% (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
 
-import Ubiq
+#include "HsVersions.h"
 
-import HsSyn		( DefaultDecl(..), MonoType,
-			  HsExpr, HsLit, ArithSeqInfo, Fake, InPat)
-import RnHsSyn		( RenamedDefaultDecl(..) )
-import TcHsSyn		( TcIdOcc )
+import HsSyn		( HsDecl(..), DefaultDecl(..) )
+import RnHsSyn		( RenamedHsDecl )
 
-import TcMonad		hiding ( rnMtoTcM )
-import Inst		( InstOrigin(..) )
-import TcEnv		( tcLookupClassByKey )
-import TcMonoType	( tcMonoType )
+import TcMonad
+import TcEnv		( tcLookupClassByKey_maybe )
+import TcMonoType	( tcHsType )
 import TcSimplify	( tcSimplifyCheckThetas )
 
-import PrelInfo		( intTy, doubleTy, unitTy )
+import TysWiredIn	( integerTy, doubleTy )
+import Type             ( Type )
 import Unique		( numClassKey )
+import ErrUtils		( addShortErrLocLine )
+import Outputable
 import Util
 \end{code}
 
 \begin{code}
-tcDefaults :: [RenamedDefaultDecl]
+default_default = [integerTy, doubleTy]
+
+tcDefaults :: [RenamedHsDecl]
 	   -> TcM s [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
 
-tcDefaults []
-  = returnTc [intTy, doubleTy] 	    -- language-specified default `default'
+tc_defaults [DefaultDecl [] locn]
+  = returnTc []		-- no defaults
 
-tcDefaults [DefaultDecl mono_tys locn]
-  = tcAddSrcLoc locn $
-    mapTc tcMonoType mono_tys	`thenTc` \ tau_tys ->
+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 [] ;
 
-    case tau_tys of
-      [] -> returnTc []		-- no defaults
+	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
+    }
+
+tc_defaults decls@(DefaultDecl _ loc : _) =
+    tcAddSrcLoc loc $
+    failWithTc (dupDefaultDeclErr decls)
 
-	tcLookupClassByKey numClassKey			`thenNF_Tc` \ num ->
-	tcSimplifyCheckThetas DefaultDeclOrigin
-		[ (num, ty) | ty <- tau_tys ]		`thenTc` \ _ ->
 
-	returnTc tau_tys
+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)
+  = hang (ptext SLIT("Multiple default declarations"))
+      4  (vcat (map pp dup_things))
+  where
+    pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
 \end{code}
+