Haskell programming language

Haskell is… Memory managed (allocation, collection) “Typeful” (static, strong) Types are checked at compile-time Types cannot be coerced (in general) Pure functional programming Emphasis on functions Referential transparency All variables are constant

Haskell - pros & cons Concurrency The #1 on Language Shootout for threading All non-I/O code is concurrent by default (mutations are handled as I/O code) Readability No parentheses or commas Higher-order functions reduce lines-of-code (no syntax as a reminder of context)

Haskell - namespaces Main main True a Bool Eq -- modules (packages) -- value variables (functions) -- value constructors -- type variables (generics) -- type constructors -- type classes (interfaces)

Haskell - syntax Derived syntax f x = expr (x *) (* y) (*) x `times` y f $ g $ h x (f . g . h) x do a; b; c Core syntax f = \x -> expr \y -> x * y \x -> x * y \x y -> x * y times x y f (g (h x)) a >>= b >>= c -- lambda -- sections -- infix func -- parens -- compose -- I/O bind

Haskell - type syntax life = 42 :: Int life :: Int life = 42

Haskell - types “Hello” :: String length :: [a] -> Int floor :: Float -> Int map :: (a -> b) -> [a] -> [b] 42 :: Int (+) :: Int -> Int -> Int 42 :: Num a => a (+) :: Num a => a -> a -> a

Haskell - type system Int, Word, Float, Double, Char type String = [Char] data Maybe a = Nothing | Just a class Eq a where (==), (/=) :: a -> a -> Bool instance Eq Bool where True == True = True False == False = True _ == _ = False -- built-in types -- type synonyms -- data types -- type classes -- type class instances

Haskell - datatypes -- enumerations -- generics -- unlabeled record data Bool = False | True data Tree a = Leaf a | Branch (Tree a) (Tree a) data Rect = Rect Int Int Int Int data Rect = Rect { x, y :: Int, width :: Int, height :: Int} -- enumerations -- generics -- unlabeled record -- labeled record

Haskell - example programs main = return () main = putStrLn “Hello World” main = interact id main = interact (unlines . reverse . lines) main = do args <- getArgs case args of "-n":a -> putStr (unwords a) a -> putStrLn (unwords a) -- null program -- hello world -- UNIX cat -- GNU tac -- UNIX echo

version control system

Darcs - overview The Theory of Patches A “branch” is a set of patches “Spontaneous branches” Every checkout is a branch Every checkout is a repository

Darcs - interactive Interactive “pull” You chose what patches to download Interactive “push” You chose what patches to commit externally Interactive “record” You chose what files to commit locally

Parsec parser library

Parsec - combinators many :: Parser a -> Parser [a] optional :: Parser a -> Parser (Maybe a) sepBy :: Parser a -> Parser s -> Parser [a] sepBy1 :: Parser a -> Parser s -> Parser [a] endBy :: Parser a -> Parser s -> Parser [a] endBy1 :: Parser a -> Parser s -> Parser [a] char :: Char -> Parser Char between :: Parser open -> Parser close -> Parser a -> Parser a -- like regex* -- like regex+ -- like regex? -- ... , ... , ... -- ... ; ... ; ... ; -- c -- < ... >

Parsec - example parsers number = many digit string = between (char ‘"’) (many anyChar) lisp = number <|> string <|> identifier <|> parens $ many $ lexeme lisp

xmonad X11 window manager

XMonad - overview Tilling window manager (like Ratpoison) Libraries of extensions and status bars Customizable (config file is the app) Full keyboard accessibility

XMonad - example config module Main where import XMonad import System.Exit import qualified XMonad.StackSet as W import qualified Data.Map as M myKeys conf@(XConfig {XMonad.modMask = modMask}) = M.fromList $ [ ((modMask .|. shiftMask, xK_Return), spawn $ XMonad.terminal conf), ((modMask .|. shiftMask, xK_q ), io (exitWith ExitSuccess))] myMouseBindings (XConfig {XMonad.modMask = modMask}) = M.fromList $ [ ((modMask, button1), (\w -> focus w >> mouseMoveWindow w)), ((modMask, button2), (\w -> focus w >> windows W.swapMaster)), ((modMask, button3), (\w -> focus w >> mouseResizeWindow w))] defaults = defaultConfig { keys = myKeys, mouseBindings = myMouseBindings, terminal = "xterm"} main = xmonad defaults

extensible text editor Yi extensible text editor

Yi - overview Extensible Fully dynamic application (hs-plugins) All state is serialized and reloaded Customizable yi --as=vim (for vim key bindings) yi --as=emacs (for emacs key bindings)

Yi - structure Taken from <http://www.cse.unsw.edu.au/~dons/papers/SC05.html>

Haskell Thank You