.SECONDEXPANSION:

n=
s=$n    $n

FORCE: $$(info $$splanning $$@)
	$(info $srunning $@)

%.xa: $$(info $$splanning $$@) %.xb %.xc $$(if $$(wildcard $$*.xc),,$$(info $$*.xc needs touching -> $$(shell [ -r $$*.xc ] && echo 'already exists' || (sleep 1 && touch $$*.xc))))
	$(info $srunning $@)

%.xb: $$(info $$splanning $$@) FORCE
	$(info $srunning $@)

%.xc: $$(info $$splanning $$@) FORCE
	$(info $srunning $@)