recursive lambda-expressions possible?
lambda, python, recursion
Solution
Maybe you need a Y combinator?
Edit - make that a Z combinator (I hadn't realized that Y combinators are more for call-by-name)
Using the definition of the Z combinator from Wikipedia
>>> Z = lambda f: (lambda x: f(lambda *args: x(x)(*args)))(lambda x: f(lambda *args: x(x)(*args)))
Using this, you can then define add as a completely anonymous function (ie. no reference to its name in its definition)
>>> add = Z(lambda f: lambda a, b: b if a <= 0 else 1 + f(a - 1, b))
>>> add(1, 1)
2
>>> add(1, 5)
6
Problem
I'm trying to write a lambda-expression that calls itself, but i can't seem to find any syntax for that, or even if it's possible. Essentially what I wanted to transfer the following function into the following lambda expression: (I realize it's a silly application, it just adds, but I'm exploring what I can do with lambda-expressions in python) ``` def add(a, b): if a <= 0: return b else: return 1 + add(a - 1, b) add = lambda a, b: [1 + add(a-1, b), b][a <= 0] ``` but calling the lambda form of add results in a runtime error because the maximum recursion depth is reached. Is it even possible to do this in python? Or am I just making some stupid mistake? Oh, I'm using python3.0, but I don't think that should matter?