! Copyright (C) 2009 Kim Taeho. ! See http://factorcode.org/license.txt for BSD license. USING: locals sequences kernel math ; IN: euler-2 : next-fib-term ( seq -- n ) 2 tail* sum ; : next-fib-seq ( seq -- newseq ) dup next-fib-term suffix ; : exceeds-limit? ( seq -- ? ) peek 4000000 > ; :: fib-seq ( seq -- newseq ) seq next-fib-term exceeds-limit? [ seq ] [ seq next-fib-seq fib-seq ] if ; : solve ( -- n ) { 1 2 } fib-seq [ even? ] filter sum ;