# I have no control over this action, performed by a third party compiler
define third_party_compiler
	rm -fr sub
	mkdir -p sub
	touch sub/Makefile.SH
	echo 'if [ ! -f config.sh ]; then echo "config.sh missing"; exit 1; fi' >> sub/Makefile.SH
	echo '. ./config.sh' >> sub/Makefile.SH
	echo 'echo "default: ; touch final" >>Makefile' >> sub/Makefile.SH
	touch $@
endef

sub/final: sub/Makefile
	$(MAKE) -C $(<D)

sub/Makefile: sub/Makefile.SH sub/config.sh
	cd $(<D) && sh Makefile.SH

sub/config.sh: | sub/Makefile.SH
	touch $@

sub/Makefile.SH: epr ;

epr: source
	$(third_party_compiler)

source:
	touch $@

clean:
	rm -f epr source
	rm -fr sub