Using data types for complex function arguments

dog.hs

#!/usr/bin/env runhaskell

import Control.Monad (replicateM_)

data Dog = Dog {
		name :: String,
		breed :: String,
		barks :: Int
	}

defaultDog :: Dog
defaultDog = Dog {
		name = "Dog",
		breed = "Beagle",
		barks = 2
	}

bark :: Dog -> IO ()
bark dog = replicateM_ (barks dog) $ putStrLn $ (name dog) ++ " (" ++ (breed dog) ++ "): Ruff!"

main :: IO ()
main = do
	bark $ defaultDog {
			name = "Snoopy",
			barks = 2
		}

	bark $ defaultDog {
			name = "Wishbone",
			breed = "Terrier",
			barks = 3
		}

Adding

{-# LANGUAGE RecordWildCards #-}

on top of code (after hash-bang line), you can then write

bark :: Dog -> IO ()
bark Dog{..} = replicateM_ barks $ putStrLn $ name ++ " (" ++ breed ++ "): Ruff!"

Thanks, Persson. That's pretty handy.