APL Hacking: Project Euler Daily (#2)

For this one, I could not come up with a solution that did not have a loop in it, but I tried to make that loop as simple as possible.

Problem #2:

∇R←PETWO;X;⎕IO
⎕IO←1
⍝ Find the sum of all even fibonacci numbers < 4,000,000

X←0 1

:Repeat

X←X,X[⍴X]+X[(⍴X)-1]

:Until X[⍴X]>4000000

R←+/(0=2|X)/X

∇