S:=simple
R=recursive
SE:=
RE=
foo=FOO
bar=
S+=$(foo) $(bar)
R+=$(foo) $(bar)
SE+=$(foo) $(bar)
RE+=$(foo) $(bar)
U+=$(foo) $(bar)
bar=BAR
test:
echo "$(S)"
echo "$(R)"
echo "$(SE)"
echo "$(RE)"
echo "$(U)"
echo "$(flavor S)"
echo "$(flavor R)"
echo "$(flavor SE)"
echo "$(flavor RE)"
echo "$(flavor U)"