[project @ 2003-06-27 21:17:24 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcRules.lhs

diff --git a/ghc/compiler/typecheck/TcRules.lhs b/ghc/compiler/typecheck/TcRules.lhs
index 533971f..a26faa8 100644 (file)
--- a/ghc/compiler/typecheck/TcRules.lhs
+++ b/ghc/compiler/typecheck/TcRules.lhs
@@ -15,11 +15,12 @@ import TcHsSyn              ( TypecheckedRuleDecl, mkHsLet )
 import TcRnMonad
 import TcSimplify      ( tcSimplifyToDicts, tcSimplifyInferCheck )
 import TcMType         ( newTyVarTy )
+import TcUnify         ( Expected(..) )
 import TcType          ( tyVarsOfTypes, openTypeKind )
-import TcIfaceSig      ( tcCoreExpr, tcCoreLamBndrs, tcVar )
+import TcIfaceSig      ( tcCoreExpr, tcCoreLamBndrs )
 import TcMonoType      ( tcHsSigType, UserTypeCtxt(..), tcAddScopedTyVars )
-import TcExpr          ( tcMonoExpr )
-import TcEnv           ( tcExtendLocalValEnv )
+import TcExpr          ( tcCheckRho )
+import TcEnv           ( tcExtendLocalValEnv, tcLookupGlobalId, tcLookupId )
 import Inst            ( instToId )
 import Id              ( idType, mkLocalId )
 import Outputable
@@ -33,14 +34,21 @@ tcRule :: RenamedRuleDecl -> TcM TypecheckedRuleDecl
 tcRule (IfaceRule name act vars fun args rhs src_loc)
   = addSrcLoc src_loc          $
     addErrCtxt (ruleCtxt name) $
-    tcVar fun                          `thenM` \ fun' ->
+    tcLookupGlobalId fun               `thenM` \ fun' ->
     tcCoreLamBndrs vars                        $ \ vars' ->
     mappM tcCoreExpr args              `thenM` \ args' ->
     tcCoreExpr rhs                     `thenM` \ rhs' ->
     returnM (IfaceRuleOut fun' (Rule name act vars' args' rhs'))
 
-tcRule (IfaceRuleOut fun rule) -- Built-in rules come this way
-  = tcVar fun                          `thenM` \ fun' ->
+tcRule (IfaceRuleOut fun rule) -- Built-in rules, and only built-in rules, 
+                               -- come this way.  Usually IfaceRuleOut is only
+                               -- used for the *output* of the type checker
+  = tcLookupId fun             `thenM` \ fun' ->
+       -- NB: tcLookupId, not tcLookupGlobalId
+       -- Reason: when compiling GHC.Base, where eqString is defined,
+       --         we'll get the builtin rule for eqString, but eqString
+       --         will be in the *local* type environment.
+       -- Seems like a bit of a hack
     returnM (IfaceRuleOut fun' rule)   
 
 tcRule (HsRule name act vars lhs rhs src_loc)
@@ -56,8 +64,8 @@ tcRule (HsRule name act vars lhs rhs src_loc)
        tcExtendLocalValEnv ids                 $
        
                -- Now LHS and RHS
-       getLIE (tcMonoExpr lhs rule_ty)         `thenM` \ (lhs', lhs_lie) ->
-       getLIE (tcMonoExpr rhs rule_ty)         `thenM` \ (rhs', rhs_lie) ->
+       getLIE (tcCheckRho lhs rule_ty) `thenM` \ (lhs', lhs_lie) ->
+       getLIE (tcCheckRho rhs rule_ty) `thenM` \ (rhs', rhs_lie) ->
        
        returnM (ids, lhs', rhs', lhs_lie, rhs_lie)
     )                          `thenM` \ (ids, lhs', rhs', lhs_lie, rhs_lie) ->
@@ -86,17 +94,16 @@ tcRule (HsRule name act vars lhs rhs src_loc)
        --      RULE:  forall v. fst (ss v) = fst v
        -- The type of the rhs of the rule is just a, but v::(a,(b,c))
        --
-       -- It's still conceivable that there may be type variables mentioned
-       -- in the LHS, but not in the type of the lhs, nor in the binders.
-       -- They'll get zapped to (), but that's over-constraining really.
-       -- Let's see if we get a problem.
+       -- We also need to get the free tyvars of the LHS; but we do that
+       -- 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) ->