1. Haskell
Chapter 9

2. More Input and More Output
Files and Streams
Transforming Input
Randomness
Not covered
brackets
command-line arguments
bytestrings

3. Reading a file – brute force
import System.IO
main3 = do
handle <- openFile "haiku.txt" ReadMode
contents <- hGetContents handle
putStr contents
putStr "\n"
hClose handle
openFile :: FilePath -> IOMode -> IO Handle
type FilePath = String
data IOMode = ReadMode | WriteMode | AppendMode | ReadWriteMode

4. Reading a file – simpler
import System.IO
main4 = do
contents <- readFile "haiku.txt"
putStr contents
putStr "\n"
readFile :: FilePath -> String -> IO()
Haiku (from wikipedia)
Japanese poetry
Essence is “cutting”
Traditional has 17 on (syllables) in 3 phrases, with syllables/phrase

5. Transforming input Common pattern*: get string from input transform
output result
lines & unlines – convert between lines separated by \n and array
Prelude> lines "aa\nbb\nbb"
["aa","bb","bb"]
Prelude> unlines ["the","brown","cow","says","moo"]
"the\nbrown\ncow\nsays\nmoo\n"
*Haskell has a feature named interact that does this. Doesn’t work well on all machines, so we’re not covering.

6. More examples words & unwords Prelude> words "Never trust a llama"
Prelude> unwords ["the","cat","in","the","hat"]
"the cat in the hat“
*Main> unwords $ reverse $ words "this is it"
"it is this"

7. Another example
isPal :: String -> Bool isPal xs = xs == reverse xs *Main> map isPal $ words "civic radar banana racecar apple" [True,True,False,True,False]
Review: what’s the purpose of $

8. Randomness
Referential transparency: function given the same parameters twice must return same result
SO, we bring in randomness from outside (kind of like using Unix time stamp for a seed)
Take a random generator, return a random value and new random generator
random : : (RandomGen g, Random a) => g -> (a, g)
Take an integer, return a random generator
mkStdGen :: Int -> StdGen
* more random functions in book

9. Example
import System.Random threeCoins :: StdGen -> (Bool, Bool, Bool) threeCoins gen = let (firstCoin, newGen) = random gen (secondCoin, newGen') = random newGen (thirdCoin, newGen'') = random newGen' in (firstCoin, secondCoin, thirdCoin) --threeCoins (mkStdGen 22)