Haskell

1
Haskell

• programming language

2
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

3
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)

4
Haskell - namespaces

• Main
• main
• True
• a
• Bool
• Eq

• -- modules (packages)
• -- value variables (functions)
• -- value constructors
• -- type variables (generics)
• -- type constructors
• -- type classes (interfaces)

5
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 -gt expr \y -gt x y \x -gt x
y \x y -gt x y times x y f (g (h x)) f (g (h
x)) a gtgt b gtgt c
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Haskell - type syntax

• life 42 Int
• life Int
• life 42

7
Haskell - types

• Hello String
• length a -gt Int
• floor Float -gt Int
• map (a -gt b) -gt a -gt b
• 42 Int
• () Int -gt Int -gt Int
• 42 Num a gt a
• () Num a gt a -gt a -gt a

8
Haskell - type system

• Int, Word, Float, Double, Char
• type String Char
• data Maybe a Nothing Just a
• class Eq a where
• (), (/) a -gt a -gt Bool
• instance Eq Bool where
• True True True
• False False True
• _ _ False

• -- built-in types
• -- type synonyms
• -- data types
• -- type classes
• -- type class instances

9
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

10
Haskell - example programs

• main return ()
• main putStrLn Hello World
• main interact id
• main interact
• (unlines . reverse . lines)
• main do
• args lt- getArgs
• case args of
• "-n"a -gt putStr (unwords a)
• a -gt putStrLn (unwords a)

• -- null program
• -- hello world
• -- UNIX cat
• -- GNU tac
• -- UNIX echo

11

• version control system

12
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

13
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

14
Parsec

• parser library

15
Parsec - combinators

• many Parser a -gt Parser a
• many1 Parser a -gt Parser a
• optional Parser a -gt Parser (Maybe a)
• sepBy Parser a -gt Parser s -gt Parser a
• sepBy1 Parser a -gt Parser s -gt Parser a
• endBy Parser a -gt Parser s -gt Parser a
• endBy1 Parser a -gt Parser s -gt Parser a
• char Char -gt Parser Char
• between Parser open
• -gt Parser close
• -gt Parser a -gt Parser a

• -- like regex
• -- like regex
• -- like regex?
• -- ... , ... , ...
• -- ... ... ...
• -- c
• -- lt ... gt

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Parsec - example parsers

• number many digit
• string between
• (char ")
• (char ")
• (many anyChar)
• lisp number
• ltgt string
• ltgt identifier
• ltgt parens many lexeme lisp

17
xmonad

• X11 window manager

18
XMonad - overview

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

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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_at_(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 -gt focus w gtgt
  mouseMoveWindow w)),
• ((modMask, button2), (\w -gt focus w gtgt
  windows W.swapMaster)),
• ((modMask, button3), (\w -gt focus w gtgt
  mouseResizeWindow w))
• defaults defaultConfig
• keys myKeys,
• mouseBindings myMouseBindings,

20
Yi

• extensible text editor

21
Yi - overview

• Extensible
• Fully dynamic application (hs-plugins)
• All state is serialized and reloaded
• Customizable
• yi --asvim (for vim key bindings)
• yi --asemacs (for emacs key bindings)

22
Yi - structure
Taken from lthttp//www.cse.unsw.edu.au/dons/paper
s/SC05.htmlgt
23
Haskell

• Thank You