Haskell @ HAN Arnhem 2013-2014
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This document provides an introduction and overview of the Haskell programming language. It discusses: - The speaker's background and an introduction to Simon Peyton Jones, a researcher at Microsoft. - An overview of what Haskell is - a purely functional, lazy, higher-order, strongly typed general purpose language. - Why learning Haskell is useful even if you don't use it primarily - it encourages different thinking that can improve programming in any language. - A brief history of the development of Haskell and how it has evolved over time through various versions. - Examples of real-world applications of Haskell like text tools, GUI programming, databases, networking, and the tiling window manager xmonad
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Haskell @ HAN Arnhem 2013-2014
- 1. Haskell Tjeerd Hans Terpstra Microsoft Consultant Atos
- 2. Agenda • Introduction • History of Haskell • Real world Haskell • I/O • Step back • Project Euler
- 3. Introduction – who? • Microsoft Consultant @ Atos • Microsoft Competence Leader for Atos East NL • Developer, Team lead, Scrum Master @tjeerdhans
- 4. Introduction – who too? Simon Peyton Jones Researcher at Microsoft Research (Cambridge, England) http://research.microsoft.com/en-us/people/simonpj/ • A Taste of Haskell - http://research.microsoft.com/enus/um/people/simonpj/papers/haskell-tutorial/index.htm
- 5. Introduction – what? • Haskell is a programming language that is • • • • • purely functional lazy higher order strongly typed general purpose
- 6. Introduction – why? • Functional programming will make you think differently about programming • Mainstream languages are all about state • Functional programming is all about values • Whether or not you drink the Haskell whisky, you'll be a better programmer in whatever language you regularly use.
- 9. History of Haskell 3
- 10. History of Haskell 4
- 11. © xkcd http://xkcd.com/1312/ Real world Haskell
- 12. Real world Haskell • Text-based tools • Imperative input/output programming • Parsing, transforming data • GUI programming • Event driven programming • Hook up events to callback functions in Haskell • Database programming • Network programming • Examples: http://book.realworldhaskell.org/read
- 13. Real world Haskell – xmonad • xmonad is an X11 tiling window manager written entirely in Haskell … xmo..-wut?! DEMO!
- 14. Real world Haskell – xmonad • xmonad is an X11 tiling window manager written entirely in Haskell
- 15. Why xmonad? • Because it's • • • • • A real program of manageable size that illustrates many Haskell programming techniques is open-source software is being actively developed by an active community
- 17. Inside xmonad
- 26. Things to notice • Purity makes the interface explicit • Takes a stack, and returns a stack; that is all • Takes a stack; may modify it; may modify other persistent state; may do I/O
- 27. I/O
- 28. Where’s the I/O in xmonad? • All this pure stuff is nice, but sooner or later we have to: • Talk to X11, whose interface is not at all pure • Do input/output (other programs)
- 29. Doing I/O • Idea: • But: now might do arbitrary stateful things • And what does this do? • What order are the things printed? • Are they printed at all? Order of evaluation! Laziness!
- 30. The main idea A value of type (IO t) is an “action” that, when performed, may do some input/output before delivering a result of type t
- 31. A helpful picture A value of type (IO t) is an “action” that, when performed, may do some input/output before delivering a result of type t
- 32. Simple I/O getLine :: IO String putStr :: String -> IO () Main program is an action of type IO () main :: IO () Main = putStr “Hello World”
- 33. Connecting actions up Goal: read a line and then write it back out
- 34. Connecting actions up We have connected two actions to make a new, bigger action.
- 35. Getting two lines We want to just return (s1,s2)
- 37. Taking a step back The central challenge
- 38. The challenge of effects
- 40. Thanks
Editor's Notes
- I stole most of the slidesfromSPJ’s excellent ‘A taste of Haskell’ introduction, so a lot of credit goestohim.
- Examples?Why not obvious? (side effects, purity, laziness)
- Databases : Haskell Database Connectivity
- new term: alt-shift-enterLayout modes: alt-spaceKill window: alt-shift-cMove focus: alt-j, alt-kglxgears
- FFI = Foreignfunction interface
- Implement ‘insert’ later togetherwith the whole class.
- How do you guys think you can test Haskell programs?
- DEMO> import Test.QuickCheck
- Why might that do arbitrary stateful things?
- () = unit, lege tuple“Actions” sometimes called “computations”An action is a first class valueEvaluating an action has no effect; performing the action has an effect
- () = unit, lege tuple“Actions” sometimes called “computations”An action is a first class valueEvaluating an action has no effect; performing the action has an effect
- Plan ACode contracts, spec#By using parallel concepts (reactive extensions, linq), the need for better control over effects becomes greater (atomic actions)Plan BSelectively allow side effects (monads, e.g. IO)
- Do Euler 1 andmaybe 2 togetherwith the whole class.