Unfortunately my code is giving me an Integer Overflow exception.
(defn even-fib-sum [n]
(reduce +
(filter even?
(take n (map first (iterate (fn [[x y]] [y (+ x y)]) [0 1]))))))
The problem occurs when I call the function and pass the value 4000000
(even-fib-sum 4000000) -> throws exception
(even-fib-sum 40) -> 82790070
use +' instead of + to get auto promoting addition to bigintegers
(reduce +'
(filter even?
(take n (map first (iterate (fn [[x y]] [y (+' x y)]) [0 1])))))
Cloujure uses longs by default and treats overflow as an error. In the very early days of the language auto-promotion was the default until it was generally agreed that overflowing a long was almost always a bug except in the cases where people explicitly know they want it so it was changed and the +', *', and -' operators where added for the cases where people explicitly choose them