X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcDefaults.lhs;h=82290dbe4643f8011183136a4d99b1dd91fbdeef;hb=ac04a368e76592978fde8cc1881312f3d5db8d79;hp=811f04b6ad4c20312c938a15846c8ece7b178472;hpb=e7d21ee4f8ac907665a7e170c71d59e13a01da09;p=ghc-hetmet.git

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index 811f04b..82290db 100644
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,67 +1,79 @@
 %
-% (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 TcMonad
-import AbsSyn
+#include "HsVersions.h"
 
-import AbsPrel		( intTy, doubleTy, unitTy )
-import AbsUniType	( UniType
-			  IF_ATTACK_PRAGMAS(COMMA cmpUniType)
-			)
-import CE		( lookupCE, CE(..) )
-import E
-import Inst
-import Name
-import TcMonoType	( tcMonoType )
-import TcSimplify	( tcSimplifyCheckThetas )
-import TVE
-import Unique		( numClassKey, Unique )
-import Util
+import HsSyn		( DefaultDecl(..) )
+import Name		( Name )
+import TcRnMonad
+import TcEnv		( tcLookupGlobal_maybe )
+import TcMonoType	( tcHsType )
+import TcSimplify	( tcSimplifyDefault )
+import TcType           ( Type, mkClassPred, isTauTy )
+import PrelNames	( numClassName )
+import Outputable
+import HscTypes		( TyThing(..) )
 \end{code}
 
 \begin{code}
-tcDefaults :: E
-	   -> [RenamedDefaultDecl]
-	   -> TcM [UniType] 	    -- defaulting types to heave
+tcDefaults :: [DefaultDecl Name]
+	   -> TcM [Type] 	    -- defaulting types to heave
 				    -- into Tc monad for later use
 				    -- in Disambig.
 
-tcDefaults _ []
-  = returnTc [intTy, doubleTy] -- language-specified default `default'
+tcDefaults [] = returnM defaultDefaultTys
 
-tcDefaults e [DefaultDecl mono_tys locn]
-  = let
-	ce  = getE_CE  e
-	tce = getE_TCE e
-	tve = nullTVE
+tcDefaults [DefaultDecl [] locn]
+  = returnM []		-- no defaults
 
-	num_clas = lookupCE ce (PreludeClass numClassKey (panic "tcDefaults"))
-    in
-    babyTcMtoTcM (mapB_Tc (tcMonoType ce tce tve) mono_tys) `thenTc` \ tau_tys ->
+tcDefaults [DefaultDecl mono_tys locn]
+  = tcLookupGlobal_maybe numClassName	`thenM` \ maybe_num ->
+    case maybe_num of
+	Just (AClass num_class) -> common_case num_class
+	other	          	-> returnM []
+		-- 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
+      = addSrcLoc locn 		$
+    	addErrCtxt defaultDeclCtxt	$
+    	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_`
+    
+    	returnM tau_tys
 
-	-- compensate for extreme parser hack: `default ()' actually
-	-- sends the *type* () through to here.  Squash it.
-    case tau_tys of
-      [ty] | ty == unitTy -> returnTc []
+tcDefaults decls@(DefaultDecl _ loc : _) =
+    addSrcLoc loc $
+    failWithTc (dupDefaultDeclErr decls)
 
-      _  -> -- (Back to your regularly scheduled programming...)
 
-	    -- Check that all the types are instances of Num
+tc_default_ty hs_ty 
+ = tcHsType hs_ty				`thenM` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)	`thenM_`
+   returnM ty
 
-	tcSimplifyCheckThetas (DefaultDeclOrigin locn)
-			 [ (num_clas, ty) | ty <- tau_tys ] `thenTc` \ _ ->
-	    -- We only care about whether it worked or not
+defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
+		    $$ ptext SLIT("is an instance of class Num")
 
-	returnTc tau_tys -- caller will bung them into Tc monad
 
-tcDefaults _ (_:_)
-  = error "ERROR: You can only have one `default' declaration per module."
-    -- ToDo: proper error msg.
+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
+
+polyDefErr ty 
+  = hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty) 
 \end{code}
+