Can someone help to understand how closure iterator works?

[ElegantBeef]

Without it you have to provide the environment every time, if you change the 
parameters value it will finish early. Once finished it does not run the code. 
That's what finished means.
    
    
    echo it(1, 4) # not finished, prints 1
    echo it(1, 4) # not finished, prints 2
    echo it(1, 2) # finished, prints 0 due to being finished
    echo it(1, 3) # still finished
    
    
    Run