1
 2W = bad
 3X = bad
 4foo: W = ok
 5foo:: ; @echo $(W) $(X) $(Y) $(Z)
 6foo:: ; @echo $(W) $(X) $(Y) $(Z)
 7foo: X = ok
 8
 9Y = foo
10bar: foo
11bar: Y = bar
12
13Z = nopat
14ifdef PATTERN
15  fo% : Z = pat
16endif