gistfile2.txt

[..e/nick/dev/haskell/markov]$ ghci
GHCi, version 6.12.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Prelude> :l markov.hs 
[1 of 1] Compiling Main             ( markov.hs, interpreted )
Ok, modules loaded: Main.
*Main> let x = markovChain 1 5
Loading package old-locale-1.0.0.2 ... linking ... done.
Loading package time-1.1.4 ... linking ... done.
Loading package random-1.0.0.2 ... linking ... done.
*Main> x
[-5,-1]
*Main> x
[-5,-1]
*Main> x
[7,1]
*Main> 

markov.hs

import System.Random

--randomNegate :: (Integral a) => a -> IO a
--markovMain :: (Integral a) => a a -> [a a]
--markovChain :: (Integral a) => a a -> [a a]

randomNegate magnitude = do
    rand <- randomIO :: IO Bool
    if rand
       then return $ negate magnitude
       else return magnitude

markovMain initial range n = do
    up_or_down <- randomNegate 1
    let n1 = n + up_or_down
    if (n1 > (initial + range)) || (n1 < (initial - range))
       then return [n1, up_or_down]
       else markovMain initial range n1

-- markovMain expects `initial range n`, but n starts at initial
markovChain initial range = markovMain initial range initial