+ -- It's useful to bind bndr to scrut, rather than to a fresh
+ -- binding x = Con arg1 .. argn
+ -- because very often the scrut is a variable, so we avoid
+ -- creating, and then subsequently eliminating, a let-binding
+ -- BUT, if scrut is a not a variable, we must be careful
+ -- about duplicating the arg redexes; in that case, make
+ -- a new con-app from the args
+ bind_case_bndr env
+ | isDeadBinder bndr = return env
+ | exprIsTrivial scrut = return (extendIdSubst env bndr (DoneEx scrut))
+ | otherwise = do { dc_args <- mapM (simplVar env) bs
+ -- dc_ty_args are aready OutTypes,
+ -- but bs are InBndrs
+ ; let con_app = Var (dataConWorkId dc)
+ `mkTyApps` dc_ty_args
+ `mkApps` dc_args
+ ; simplNonRecX env bndr con_app }
+