# By considering the terms in the Fibonacci sequence whose values do not
# exceed four million, find the sum of the even-valued terms.
# https://projecteuler.net/problem=2

[ 1 2 ]

[ [ a b ] : a b a b + ] [ fib-once ] def

[ 4 1000 * 1000 * ] [ 4_million ] def

[ dup last 4_million gt? ] [ [ fib-once ] doin ] while

[ even? ] filter

[ dup length 1 lt? ] [ [ + ] doin ] while

unquote println