euler2.opa

type fib = iter(int)
 
MAX = 4000000
 
function fib fibs_init(a,b) {
    { next : function () { some((a, fibs_init(b, a+b))) } }
}
 
fib fibs = fibs_init(1,2)
 
fib even_fibs = Iter.filter(function (elm){ mod(elm, 2) == 0 }, fibs)
 
fib even_fibs_under_max = Iter.take_while(function (elm){ elm < MAX } , even_fibs)
 
jlog( Int.to_string(Iter.fold(function (elm, acc){ elm + acc }, even_fibs_under_max, 0)) )