recursively perform casting via typecases when specializing case alternatives
recursively perform casting via typecases when specializing case alternatives

darcs-hash:20070517013712-1a7c6-f3e7bdcf612c1be111afdc9aed3ab326cfde1909

kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc