X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcRules.lhs;h=e4898708d8eafe23ebd8e0ed6c029e74861fa46b;hb=e9f9ec1e57d53b9302a395ce0d02c0fa59e28341;hp=ef8e388f8706eb1b4ff0e8988a50532d6bdc4afc;hpb=ab22f4e6456820c1b5169d75f5975a94e61f54ce;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcRules.lhs b/compiler/typecheck/TcRules.lhs
index ef8e388..e489870 100644
--- a/compiler/typecheck/TcRules.lhs
+++ b/compiler/typecheck/TcRules.lhs
@@ -8,8 +8,6 @@ TcRules: Typechecking transformation rules
 \begin{code}
 module TcRules ( tcRules ) where
 
-#include "HsVersions.h"
-
 import HsSyn
 import TcRnMonad
 import TcSimplify
@@ -23,29 +21,44 @@ import Id
 import Name
 import SrcLoc
 import Outputable
+import FastString
 \end{code}
 
+Note [Typechecking rules]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+We *infer* the typ of the LHS, and use that type to *check* the type of 
+the RHS.  That means that higher-rank rules work reasonably well. Here's
+an example (test simplCore/should_compile/rule2.hs) produced by Roman:
+
+   foo :: (forall m. m a -> m b) -> m a -> m b
+   foo f = ...
+
+   bar :: (forall m. m a -> m a) -> m a -> m a
+   bar f = ...
+
+   {-# RULES "foo/bar" foo = bar #-}
+
+He wanted the rule to typecheck.
+
 \begin{code}
 tcRules :: [LRuleDecl Name] -> TcM [LRuleDecl TcId]
-tcRules decls = mappM (wrapLocM tcRule) decls
+tcRules decls = mapM (wrapLocM tcRule) decls
 
 tcRule :: RuleDecl Name -> TcM (RuleDecl TcId)
 tcRule (HsRule name act vars lhs fv_lhs rhs fv_rhs)
-  = addErrCtxt (ruleCtxt name)			$
-    traceTc (ptext SLIT("---- Rule ------")
-		 <+> ppr name)			`thenM_` 
-    newFlexiTyVarTy openTypeKind		`thenM` \ rule_ty ->
+  = addErrCtxt (ruleCtxt name)			$ do
+    traceTc (ptext (sLit "---- Rule ------") <+> ppr name)
 
 	-- Deal with the tyvars mentioned in signatures
-    tcRuleBndrs vars (\ ids ->
-		-- Now LHS and RHS
-	getLIE (tcMonoExpr lhs rule_ty)	`thenM` \ (lhs', lhs_lie) ->
-	getLIE (tcMonoExpr rhs rule_ty)	`thenM` \ (rhs', rhs_lie) ->
-	returnM (ids, lhs', rhs', lhs_lie, rhs_lie)
-    )				`thenM` \ (ids, lhs', rhs', lhs_lie, rhs_lie) ->
+    (ids, lhs', rhs', lhs_lie, rhs_lie, rule_ty) <-
+      tcRuleBndrs vars $ \ ids -> do
+		-- Now LHS and RHS; see Note [Typechecking rules]
+        ((lhs', rule_ty), lhs_lie) <- getLIE (tcInferRho lhs)
+        (rhs', rhs_lie) <- getLIE (tcMonoExpr rhs rule_ty)
+        return (ids, lhs', rhs', lhs_lie, rhs_lie, rule_ty)
 
 		-- Check that LHS has no overloading at all
-    tcSimplifyRuleLhs lhs_lie	`thenM` \ (lhs_dicts, lhs_binds) ->
+    (lhs_dicts, lhs_binds) <- tcSimplifyRuleLhs lhs_lie
 
 	-- Gather the template variables and tyvars
     let
@@ -72,24 +85,23 @@ tcRule (HsRule name act vars lhs fv_lhs rhs fv_rhs)
 	-- during zonking (see TcHsSyn.zonkRule)
 	--
 	forall_tvs = tyVarsOfTypes (rule_ty : map idType tpl_ids)
-    in
+
 	-- RHS can be a bit more lenient.  In particular,
 	-- we let constant dictionaries etc float outwards
 	--
 	-- NB: tcSimplifyInferCheck zonks the forall_tvs, and 
 	--     knocks out any that are constrained by the environment
-    tcSimplifyInferCheck (text "tcRule")
-			 forall_tvs
-			 lhs_dicts rhs_lie	`thenM` \ (forall_tvs1, rhs_binds) ->
-    mappM zonkQuantifiedTyVar forall_tvs1 	`thenM` \ forall_tvs2 ->
-	-- This zonk is exactly the same as the one in TcBinds.tcBindWithSigs
-
-    returnM (HsRule name act
-		    (map (RuleBndr . noLoc) (forall_tvs2 ++ tpl_ids))	-- yuk
+    loc <- getInstLoc (SigOrigin (RuleSkol name))
+    (forall_tvs1, rhs_binds) <- tcSimplifyInferCheck loc
+                                        forall_tvs
+                                        lhs_dicts rhs_lie
+
+    return (HsRule name act
+		    (map (RuleBndr . noLoc) (forall_tvs1 ++ tpl_ids))	-- yuk
 		    (mkHsDictLet lhs_binds lhs') fv_lhs
 		    (mkHsDictLet rhs_binds rhs') fv_rhs)
 
-
+tcRuleBndrs :: [RuleBndr Name] -> ([Id] -> TcM a) -> TcM a
 tcRuleBndrs [] thing_inside = thing_inside []
 tcRuleBndrs (RuleBndr var : vars) thing_inside
   = do 	{ ty <- newFlexiTyVarTy openTypeKind
@@ -100,7 +112,7 @@ tcRuleBndrs (RuleBndrSig var rn_ty : vars) thing_inside
 --  e.g 	x :: a->a
 --  The tyvar 'a' is brought into scope first, just as if you'd written
 --		a::*, x :: a->a
-  = do	{ let ctxt = RuleSigCtxt (unLoc var)
+  = do	{ let ctxt = FunSigCtxt (unLoc var)
 	; (tyvars, ty) <- tcHsPatSigType ctxt rn_ty
 	; let skol_tvs = tcSkolSigTyVars (SigSkol ctxt) tyvars
 	      id_ty = substTyWith tyvars (mkTyVarTys skol_tvs) ty
@@ -109,7 +121,8 @@ tcRuleBndrs (RuleBndrSig var rn_ty : vars) thing_inside
 	  tcExtendIdEnv [id] $
 	  tcRuleBndrs vars (\ids -> thing_inside (id:ids)) }
 
-ruleCtxt name = ptext SLIT("When checking the transformation rule") <+> 
+ruleCtxt :: FastString -> SDoc
+ruleCtxt name = ptext (sLit "When checking the transformation rule") <+> 
 		doubleQuotes (ftext name)
 \end{code}