The lisp-way to solve Fibonnaci

Question

I wanted to try and learn Lisp, but I very quickly gave up. I figured I\'d try again. I\'m looking at Problem 2 on Project Euler - finding the sum of all even Fibonacci numbers

Answer 1

Use tail recursion instead of naive recursion. Most Lisp implementations should perform the tailcall-optimization; no more recursion depth limit.

Beyond that, try to think of things in terms of lists and abstract operations you could perform on those lists. Two of the more relevant operations to consider:

• filter
• fold

Regarding other Lisp resources:

• Common Lisp—On Lisp
• Scheme—Structure and Interpretation of Computer Programs

UPDATE: Tail-recursive Scheme fib function:

(define (fib n)
  (fib-tr n 1 0))

(define (fib-tr n next result)
  (cond ((= n 0) result)
        (else (fib-tr (- n 1) (+ next result) next))))