dl_pack/unknown=$(error ERROR: Unknown pack format for file $(1))
define dl_pack
$(if $(dl_pack/$(call ext,$(1))),$(dl_pack/$(call ext,$(1))),$(dl_pack/unknown))
dl_pack/unknown=$(error ERROR: Unknown pack format for file $(1))
define dl_pack
$(if $(dl_pack/$(call ext,$(1))),$(dl_pack/$(call ext,$(1))),$(dl_pack/unknown))