def if__(cond, then, else_=lambda: None):
    if cond:
        return then()
    else:
        return else_()

def for__(iterable, body):
    for i in iterable:
        body(i)

def while__(cond_block, body):
    while cond_block():
        body()

def with__(obj, body):
    obj.__enter__()
    body(e)
    obj.__exit__()

def discard__(obj):
    pass

def then__(x, f):
    if x == None or x == NotImplemented:
        return x
    else:
        return f(x)