generator closure
int(0)
int(0)
int(1)
int(1)
int(2)
int(2)
int(3)
int(3)
int(0)
int(0)
int(1)
int(1)
int(2)
int(2)
int(3)
int(3)

plain closure:
012
012

plain generator:
int(0)
int(1)
int(2)
int(3)