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

-- lambda

-- sections

-- sections

-- sections

-- infix func

-- parens

-- compose

-- I/O bind

Core syntax

f = \x -> expr

\y -> x * y

\x -> x * y

\x y -> x * y

times x y

f (g (h x))

f (g (h x))

a >>= b >>= c

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

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]

many1 :: 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 ‘"’)

(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 XMonadimport System.Exitimport qualified XMonad.StackSet as Wimport 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

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