-- all occurences of the binder with the scrutinee variable.
scrutbndrremove (Case (Var scrut) bndr ty alts) | bndr_used = do
alts' <- mapM subs_bndr alts
- return $ Case (Var scrut) wild ty alts'
+ change $ Case (Var scrut) wild ty alts'
where
is_used (_, _, expr) = expr_uses_binders [bndr] expr
bndr_used = or $ map is_used alts