X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcDefaults.lhs;h=f10745121ea95a93f894910d7d4763fb1e77be29;hb=a465e8bda2a03163fa45976c531307faeea76490;hp=b28b07db9a695d8f73c3d00f6aff57ec2384a8fb;hpb=e5ed694b59d3f4debdf86ab44e656568ecec39c9;p=ghc-hetmet.git

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index b28b07d..f107451 100644
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -4,44 +4,48 @@
 \section[TcDefaults]{Typechecking \tr{default} declarations}
 
 \begin{code}
-module TcDefaults ( tcDefaults, defaultDefaultTys ) where
+module TcDefaults ( tcDefaults ) where
 
 #include "HsVersions.h"
 
-import HsSyn		( HsDecl(..), DefaultDecl(..) )
-import RnHsSyn		( RenamedHsDecl )
-
-import TcMonad
+import HsSyn		( DefaultDecl(..) )
+import Name		( Name )
+import TcRnMonad
 import TcEnv		( tcLookupGlobal_maybe )
 import TcMonoType	( tcHsType )
-import TcSimplify	( tcSimplifyCheckThetas )
-
-import TysWiredIn	( integerTy, doubleTy )
-import Type             ( Type )
+import TcSimplify	( tcSimplifyDefault )
+import TcType           ( Type, mkClassPred, isTauTy )
 import PrelNames	( numClassName )
 import Outputable
 import HscTypes		( TyThing(..) )
 \end{code}
 
 \begin{code}
-defaultDefaultTys = [integerTy, doubleTy]
-
-tcDefaults :: [RenamedHsDecl]
-	   -> TcM [Type] 	    -- defaulting types to heave
+tcDefaults :: [DefaultDecl Name]
+	   -> 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 defaultDefaultTys
 
-tc_defaults [DefaultDecl [] locn]
-  = returnTc []		-- no defaults
-
-tc_defaults [DefaultDecl mono_tys locn]
-  = tcLookupGlobal_maybe numClassName	`thenNF_Tc` \ maybe_num ->
+tcDefaults [] 
+  = getDefaultTys		-- No default declaration, so get the
+				-- default types from the envt; 
+				-- i.e. use the curent ones
+				-- (the caller will put them back there)
+	-- It's important not to return defaultDefaultTys here (which
+	-- we used to do) because in a TH program, tcDefaults [] is called
+	-- repeatedly, once for each group of declarations between top-level
+	-- splices.  We don't want to carefully set the default types in
+	-- one group, only for the next group to ignore them and install
+	-- defaultDefaultTys
+
+tcDefaults [DefaultDecl [] locn]
+  = returnM []			-- Default declaration specifying no types
+
+tcDefaults [DefaultDecl mono_tys locn]
+  = tcLookupGlobal_maybe numClassName	`thenM` \ maybe_num ->
     case maybe_num of
 	Just (AClass num_class) -> common_case num_class
-	other	          	-> returnTc []
+	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
@@ -49,24 +53,26 @@ tc_defaults [DefaultDecl mono_tys locn]
 		-- always sucking in Num
   where
     common_case num_class
-      = tcAddSrcLoc locn $
-    	mapTc tcHsType mono_tys	`thenTc` \ tau_tys ->
+      = 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
-    	tcAddErrCtxt defaultDeclCtxt		$
-    	tcSimplifyCheckThetas
- 		    [{- Nothing given -}]
- 		    [ (num_class, [ty]) | ty <- tau_tys ]	`thenTc_`
+    	tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys]	`thenM_`
     
-    	returnTc tau_tys
-
+    	returnM tau_tys
 
-tc_defaults decls@(DefaultDecl _ loc : _) =
-    tcAddSrcLoc loc $
+tcDefaults decls@(DefaultDecl _ loc : _) =
+    addSrcLoc loc $
     failWithTc (dupDefaultDeclErr decls)
 
 
+tc_default_ty hs_ty 
+ = tcHsType hs_ty				`thenM` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)	`thenM_`
+   returnM ty
+
 defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
 		    $$ ptext SLIT("is an instance of class Num")
 
@@ -76,5 +82,8 @@ 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}