euler02.clj

; Project Euler Problem 2
; Solution by nathan dotz - nathan (period) dotz (at sign) gmail (period) com
;
; Each new term in the Fibonacci sequence is generated by adding
; the previous two terms. By starting with 1 and 2, the first
; 10 terms will be:
; 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
; 
; Find the sum of all the even-valued terms in the sequence
; which do not exceed four million.
;

(ns euler2)

(def fib-seq
  "Generate a lazy fibonacci sequence with corecursion"
  (lazy-cat [0 1] (map + (rest fib-seq) fib-seq))
  )

(def small-fib
  "Sequence of fibonacci below 4 million"
  (take-while #(<= % 4000000) fib-seq)
  )

(def even-small-fib
  "All fibonacci nums below 4 million and even"
  (filter #(even? %) small-fib)
  )
 
(print
  (apply + even-small-fib)
  )