Programming Praxis – Correct Horse Battery Staple

In today’s Programming Praxis exercise, our goal is to generate xkcd-style passphrases consisting of four words. Let’s get started, shall we?

import Data.Char
import System.Random.Shuffle

First, we define our criteria for acceptable words, in this case lowercase words between 5 and 9 letters.

valid :: String -> Bool
valid s = length s > 4 && length s < 10 && all isLower s

Generating a passphrase is then a simple matter of loading a dictionary, filtering the valid words, shuffling them and printing the first four chosen words.

main :: IO ()
main = putStrLn . unwords . take 4 =<<
       shuffleM . filter valid . lines =<<
       readFile "en_US.dic"
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