In Scheme, how do you use lambda to create a recursive function?

Question

I\'m in a Scheme class and I was curious about writing a recursive function without using define. The main problem, of course, is that you cannot call a function within itse

Answer 1

I like this question. 'The scheme programming language' is a good book. My idea is from Chapter 2 of that book.

First, we know this:

(letrec ((fact (lambda (n) (if (= n 1) 1 (* (fact (- n 1)) n))))) (fact 5))

With letrec we can make functions recursively. And we see when we call (fact 5), fact is already bound to a function. If we have another function, we can call it this way (another fact 5), and now another is called binary function (my English is not good, sorry). We can define another as this:

(let ((another (lambda (f x) .... (f x) ...))) (another fact 5))

Why not we define fact this way?

(let ((fact (lambda (f n) (if (= n 1) 1 (* n (f f (- n 1))))))) (fact fact 5))

If fact is a binary function, then it can be called with a function f and integer n, in which case function f happens to be fact itself.

If you got all the above, you could write Y combinator now, making a substitution of let with lambda.