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)