[project @ 1998-04-27 09:04:10 by simonpj]

Fix subst_envs bug in SimplCase

diff --git a/ghc/compiler/simplCore/SimplCase.lhs b/ghc/compiler/simplCore/SimplCase.lhs
index 99e34ab..7e47bd4 100644 (file)
--- a/ghc/compiler/simplCore/SimplCase.lhs
+++ b/ghc/compiler/simplCore/SimplCase.lhs
@@ -116,7 +116,13 @@ simplCase env (Case inner_scrut inner_alts) (subst_envs, outer_alts) rhs_c resul
           rhs_c' = \env rhs -> simplExpr env rhs [] result_ty
        in
        simplCase env inner_scrut (getSubstEnvs env, inner_alts)
-                 (\env rhs -> simplCase env rhs (emptySubstEnvs, outer_alts') rhs_c' result_ty)
+                 (\env rhs -> simplCase env rhs (subst_envs, outer_alts') rhs_c' result_ty)
+                       -- We used to have "emptySubstEnvs" instead of subst_envs here,
+                       -- but that is *wrong*.  The outer_alts' still have the old
+                       -- binders from outer_alts, with un-substituted types,
+                       -- so we must keep their subst_envs with them.  It does
+                       -- no harm to the freshly-manufactured part of outer_alts',
+                       -- because it'll have nothing in the domain of subst_envs anyway
                  result_ty
                                                `thenSmpl` \ case_expr ->
        returnSmpl (mkCoLetsNoUnboxed extra_bindings case_expr)