human
I wrote the below code

    (op, new, children, leaf) = map(fns.get, ('op', 'new', 'children', 'leaf'))
    def all_rl(expr):
        if leaf(expr):
            return expr
        else:
            args = map(rule, children(expr))
            return new(op(expr), *args)
    return all_rl

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

def sall(rule, fns=basic_fns):