Project Euler Problem 009

import Control.Monad
import Control.Applicative
import Data.List
wa :: Num a => (a, a, a) -> a
wa (a,b,c) = a+b+c
prod :: Num a => (a, a, a) -> a
prod (a,b,c) = a*b*c
l :: [Integer]
l = [5..32] --bの範囲。3,5,...となり32^2>1000

--ピタゴラス数生成の漸化式
pita =  prod $ last $ filter ((==1000).wa) [(m*m-n*n,2*m*n,m*m+n*n)|m<-l,n<-l,n [(a-2*b+2*c, 2*a-b+2*c, 2*a-2*b+3*c), (a+2*b+2*c, 2*a+b+2*c, 2*a+2*b+3*c), (-a+2*b+2*c, -2*a+b+2*c, -2*a+2*b+3*c)]) pita4 :: [(Integer,Integer,Integer)]