[con] -> -- It matches exactly one constructor, so fill it in
do { tick (FillInCaseDefault case_bndr')
- ; con_alt <- mkDataConAlt con inst_tys rhs
+ ; us <- getUniquesSmpl
+ ; let (ex_tvs, co_tvs, arg_ids) =
+ dataConInstPat us con inst_tys
+ ; let con_alt = (DataAlt con, ex_tvs ++ co_tvs ++ arg_ids, rhs)
; Just (_, alt') <- simplAlt env [] case_bndr' cont con_alt
-- The simplAlt must succeed with Just because we have
-- already filtered out construtors that can't match