gistfile1.hs

fib :: ( Num t, Num t1 ) => t -> t1
fib 0 = 0
fib 1 = 1
fib n = fib (n-1) + fib (n-2)

cnl_clink :: (Num t, Num a, Ord a) => t -> [a]
cnl_clink x = let lx = fib x
              in
                if lx > 4000000 then
                    []
                else
                    [lx] ++ cnl_clink (x + 1)

problem_two :: Int
problem_two = do
  sum $ filter even $ cnl_clink 1