[project @ 2002-02-14 14:56:04 by simonpj]

---------------------------------------
	Record updates are ok for types involving
	existential data constructors, so long as the
	existential ones aren't the ones updated.
	---------------------------------------

This check was already in the type checker, but
the desugarer had an over-zealous assert.

diff --git a/ghc/compiler/deSugar/DsExpr.lhs b/ghc/compiler/deSugar/DsExpr.lhs
index 5560d36..45b02fb 100644 (file)
--- a/ghc/compiler/deSugar/DsExpr.lhs
+++ b/ghc/compiler/deSugar/DsExpr.lhs
@@ -454,7 +454,7 @@ dictionaries.
 dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty dicts [])
   = dsExpr record_expr
 
-dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty dicts rbinds)
+dsExpr expr@(RecordUpdOut record_expr record_in_ty record_out_ty dicts rbinds)
   = getSrcLocDs                        `thenDs` \ src_loc ->
     dsExpr record_expr         `thenDs` \ record_expr' ->
 
@@ -488,7 +488,9 @@ dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty dicts rbinds)
                                    src_loc)
     in
        -- Record stuff doesn't work for existentials
-    ASSERT( all (not . isExistentialDataCon) data_cons )
+       -- The type checker checks for this, but we need 
+       -- worry only about the constructors that are to be updated
+    ASSERT2( all (not . isExistentialDataCon) cons_to_upd, ppr expr )
 
        -- It's important to generate the match with matchWrapper,
        -- and the right hand sides with applications of the wrapper Id