human
I wrote the below code

    (op, new, children, leaf) = map(fns.get, ('op', 'new', 'children', 'leaf'))
    def all_rl(expr):
        if leaf(expr):
            (yield expr)
        else:
            myop = op(expr)
            argss = product(*map(brule, children(expr)))
            for args in argss:
                (yield new(myop, *args))
    return all_rl

What's a good function header?
assistant
#Here's a good function header.

def sall(brule, fns=basic_fns):