Hello all, As my first foray into the wonderful world of Haskell programming, I wrote a simple program that solves Laplace equations. The program is 44 lines, and I would greatly appreciate comments on how I could make it better, with regards to Haskell idioms, performance and readability. Cheers, Edward import Data.Array data Node = Node { isBoundary :: Bool, value :: Double } instance Show Node where show (Node True value) = show value ++ "*" show (Node False value) = show value blankArray :: Ix i => (i, i) -> a -> Array i a blankArray (a, b) x = array (a, b) [(i, x) | i <- range (a, b)] fillBox :: Ix i => (i, i) -> a -> Array i a -> Array i a fillBox (a, b) value m = m // [(i, value) | i <- range(a, b)] average :: Fractional a => [a] -> a average list = sum list / fromIntegral (length list) solve :: Array (Integer, Integer) Node -> Array (Integer, Integer) Node solve m = if maximum deltas > 0.0001 then solve n else n where n = array (min, max) [(i, solveNode i) | i <- range(min, max)] deltas = map delta $ zip (values m) (values n) delta (x, y) = abs (x - y) values a = map value $ elems a (min, max) = bounds m solveNode (a, b) = if isBoundary $ node then node else averageNode where node = m ! (a, b) averageNode = Node False $ average [value $ m ! i | i <- [(a+1,b),(a-1,b),(a,b+1),(a,b-1)]] myArray = fillBox ((3,3), (5,5)) (Node True 100) $ fillBox ((1,1), (8,8)) (Node False 0) $ blankArray ((0,0), (9,9)) (Node True 0)