[project @ 2002-09-25 11:55:07 by simonpj]

[ghc-hetmet.git] / ghc / compiler / rename / RnSource.lhs

diff --git a/ghc/compiler/rename/RnSource.lhs b/ghc/compiler/rename/RnSource.lhs
index d8c9a5b..a368122 100644 (file)
--- a/ghc/compiler/rename/RnSource.lhs
+++ b/ghc/compiler/rename/RnSource.lhs
@@ -57,8 +57,8 @@ import Outputable
 import SrcLoc          ( SrcLoc )
 import CmdLineOpts     ( DynFlag(..) )
                                -- Warn of unused for-all'd tyvars
-import Maybes          ( maybeToBool )
-import Maybe            ( maybe, catMaybes )
+import Maybes          ( maybeToBool, seqMaybe )
+import Maybe            ( maybe, catMaybes, isNothing )
 \end{code}
 
 @rnSourceDecl@ `renames' declarations.
@@ -301,7 +301,10 @@ rnHsForeignDecl (ForeignExport name ty spec isDeprec src_loc)
     lookupOccRn name                           `thenM` \ name' ->
     rnHsTypeFVs (fo_decl_msg name) ty                  `thenM` \ (ty', fvs) ->
     returnM (ForeignExport name' ty' spec isDeprec src_loc, 
-             mkFVs [bindIOName, returnIOName] `plusFV` fvs)
+             mkFVs [name', bindIOName, returnIOName] `plusFV` fvs )
+       -- NB: a foreign export is an *occurrence site* for name, so 
+       --     we add it to the free-variable list.  It might, for example,
+       --     be imported from another module
 
 fo_decl_msg name = ptext SLIT("In the foreign declaration for") <+> ppr name
 \end{code}
@@ -394,8 +397,11 @@ rnHsRuleDecl (HsRule rule_name act vars lhs rhs src_loc)
 
     rnExpr lhs                                 `thenM` \ (lhs', fv_lhs) ->
     rnExpr rhs                                 `thenM` \ (rhs', fv_rhs) ->
-    checkErr (validRuleLhs ids lhs')
-           (badRuleLhsErr rule_name lhs')      `thenM_`
+    let
+       mb_bad = validRuleLhs ids lhs'
+    in
+    checkErr (isNothing mb_bad)
+            (badRuleLhsErr rule_name lhs' mb_bad)      `thenM_`
     let
        bad_vars = [var | var <- ids, not (var `elemNameSet` fv_lhs)]
     in
@@ -415,16 +421,37 @@ rnHsRuleDecl (HsRule rule_name act vars lhs rhs src_loc)
 
 Check the shape of a transformation rule LHS.  Currently
 we only allow LHSs of the form @(f e1 .. en)@, where @f@ is
-not one of the @forall@'d variables.
+not one of the @forall@'d variables.  We also restrict the form of the LHS so
+that it may be plausibly matched.  Basically you only get to write ordinary 
+applications.  (E.g. a case expression is not allowed: too elaborate.)
+
+NB: if you add new cases here, make sure you add new ones to TcRule.ruleLhsTvs
 
 \begin{code}
+validRuleLhs :: [Name] -> RenamedHsExpr -> Maybe RenamedHsExpr
+-- Nothing => OK
+-- Just e  => Not ok, and e is the offending expression
 validRuleLhs foralls lhs
   = check lhs
   where
-    check (OpApp _ op _ _)               = check op
-    check (HsApp e1 e2)                  = check e1
-    check (HsVar v) | v `notElem` foralls = True
-    check other                                  = False
+    check (OpApp e1 op _ e2)             = check op `seqMaybe` check_e e1 `seqMaybe` check_e e2
+    check (HsApp e1 e2)                  = check e1 `seqMaybe` check_e e2
+    check (HsVar v) | v `notElem` foralls = Nothing
+    check other                                  = Just other  -- Failure
+
+    check_e (HsVar v)     = Nothing
+    check_e (HsPar e)    = check_e e
+    check_e (HsLit e)    = Nothing
+    check_e (HsOverLit e) = Nothing
+
+    check_e (OpApp e1 op _ e2)          = check_e e1 `seqMaybe` check_e op `seqMaybe` check_e e2
+    check_e (HsApp e1 e2)               = check_e e1 `seqMaybe` check_e e2
+    check_e (NegApp e _)                = check_e e
+    check_e (ExplicitList _ es)         = check_es es
+    check_e (ExplicitTuple es _) = check_es es
+    check_e other               = Just other   -- Fails
+
+    check_es es = foldr (seqMaybe . check_e) Nothing es
 \end{code}
 
 
@@ -910,9 +937,10 @@ getRnStats eps imported_decls
 badDataCon name
    = hsep [ptext SLIT("Illegal data constructor name"), quotes (ppr name)]
 
-badRuleLhsErr name lhs
+badRuleLhsErr name lhs (Just bad_e)
   = sep [ptext SLIT("Rule") <+> ftext name <> colon,
-        nest 4 (ptext SLIT("Illegal left-hand side:") <+> ppr lhs)]
+        nest 4 (vcat [ptext SLIT("Illegal expression:") <+> ppr bad_e, 
+                      ptext SLIT("in left-hand side:") <+> ppr lhs])]
     $$
     ptext SLIT("LHS must be of form (f e1 .. en) where f is not forall'd")