Finding Pythagorean Triplets

pyth_triplets.hs

import Data.List
import System.Environment

isPythTriplet :: (Integer, Integer, Integer) -> Bool
isPythTriplet (a, b, c) = (a^2) + (b^2) == (c^2)

-- All possible representations of three elements from xs,
-- where let xs[x] = indexof x in xs[a] < xs[b] < xs[c].
triplets :: [Integer] -> [(Integer, Integer, Integer)]
triplets xs = [ (a, b, c) | a:as <- tails xs,
                            b:bs <- tails as,
                            c    <- bs ]

-- Run like "$ ./pyth_triplets 1000" to find the triplets <= 1000
main = do
  args <- getArgs
  let limit = read (args !! 0) :: Integer
  print $ filter isPythTriplet (triplets [1..limit])