Thanks. Here's a newb question: what does strictness really get me in this code? BTW, I only noticed the Complex type late. I looked at it and noticed that all I'd be using is the constructor and add. Didn't seem worth the change. Michael Derek Elkins wrote:
To answer the question in your subject, yes! We have a complex type. Not only does that make the code simpler and more obvious and idiomatic, but it's also more efficient because for this use you'd really prefer a strict pair type for "Point", and complex is strict in it's components.
On Sun, 2008-07-06 at 21:02 -0400, Michael Feathers wrote:
Decided a while ago to write some code to calculate the Mandelbrot set using the escape iterations algorithm. Discovered after mulling it about that I could just built it as an infinite list of infinite lists and then extract any rectangle of values that I wanted:
type Point = (Double, Double)
sq :: Double -> Double sq x = x ^ 2
translate :: Point -> Point -> Point translate (r0, i0) (r1, i1) = (r0 + r1, i0 + i1)
mandel :: Point -> Point mandel (r, i) = (sq r + sq i, 2 * r * i)
notEscaped :: Point -> Bool notEscaped (r, i) = (sq r + sq i) <= 4.0
trajectory :: (Point -> Point) -> [Point] trajectory pointFunction = takeWhile notEscaped $ iterate pointFunction seed where seed = (0.0, 0.0)
escapeIterations :: (Point -> Point) -> Int escapeIterations = length . tail . take 1024 . trajectory
mandelbrot :: Double -> [[Int]] mandelbrot incrementSize = [[ escapeIterations $ translate (x, y) . mandel | x <- increments] | y <- increments] where increments = [0.0, incrementSize .. ]
window :: (Int, Int) -> (Int, Int) -> [[a]] -> [[a]] window (x0, y0) (x1, y1) = range x0 x1 . map (range y0 y1) where range m n = take (n - m) . drop m
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