Problem 2

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

Find the sum of all the even-valued terms in the sequence which do not exceed four million.

工夫のしどころもあるが、単純なものをさっさと書いて次の問題に行くのが良いだろう。

(工夫するの面倒ww)

p002 = sum.(takeWhile (<4000000)).(filter even) $  fib
where fib = 1:2:[x+y|(x,y)<-zip fib $tail fib]
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