Haskell Talk

A TechTalk for the SSE

Transcript

1. Haskell Chris Bentivenga http://sse.se.rit.edu/go/haskell_talk Thursday, December 20, 12
2. Go To: http://sse.se.rit.edu/go/haskell_talk Thursday, December 20, 12
3. What is Haskell? Thursday, December 20, 12
4. Haskell is a computer programming language. In particular, it is a polymorphically statically typed, lazy, purely functional language, quite different from most other programming languages. http://www.haskell.org/haskellwiki/Introduction Thursday, December 20, 12
5. Polymorphically Statically Typed •id :: a -> a •Char -> Char • Int -> Int • Bool -> Bool Thursday, December 20, 12
6. Lazy • Not evaluated when bound • Evaluated when executed • take 5 [1..] • [1,2,3,4,5] Thursday, December 20, 12
7. Purely Functional • Imperative (OO, Procedural): • Execute statements • Change state • Functional: • Evaluate expressions • No state Thursday, December 20, 12
8. Features of Functional Languages • High Order Functions • Purity • Lazy Execution • Recursion Thursday, December 20, 12
9. High Order Functions •filter odd [1,2,3,4,5,6,7] •[1,3,5,7] •filter sq [1,2,3,4,5,6,7] •[2,4] Thursday, December 20, 12
10. Purity • No side effects • Is no state • A function, given the same input will always return the same output • Haskell does have monads • Used to simulate side effects Thursday, December 20, 12
11. Lazy • Not evaluated when bound • Evaluated when executed • take 5 [1..] • [1,2,3,4,5] Already Saw This! Thursday, December 20, 12
12. Recursion • Same as recursion in any other paradigim • One of the few ways to iterate • Is no for loop Thursday, December 20, 12
13. Getting Started in Haskell Thursday, December 20, 12
14. 3 Haskell Commands • ghc • Compiler (gcc, g++) • ghci • Interactive (python <no args>, irb) • REPL • runghc • Run as interpreted (python <file>, ruby) Thursday, December 20, 12
15. Haskell Basics • Entry point: main function (like C, C++) • Basic output function: print Thursday, December 20, 12
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18. Haskell Functions Thursday, December 20, 12
19. Silly Silly Haskell Notation • $ -- Function Applicator • . -- Function Composition Thursday, December 20, 12
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21. Currying • Partially fill out the parameters on a function • Creates a new function that expects fewer paramaters Thursday, December 20, 12
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23. Parameters • Functions technically can’t have more then one parameter • A function with two parameters is technically a function that returns a function that accepts a parameter... Thursday, December 20, 12
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26. Typing System • Strictly typed under the hood • Don’t have to see those types • Can explicitly write out types on a function Thursday, December 20, 12
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28. /Users/chris/projects/haskell_talk/Types/types.hs:4:10: Couldn't match expected type `Int' with actual type `[Char]' In the first argument of `f', namely `"123"' In the expression: f "123" In an equation for `main': main = f "123" Thursday, December 20, 12
29. Lists • Standard functional data structure • List operations: map, filter, reduce, etc... Thursday, December 20, 12
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31. Pattern Matching • Function headers have portions already declared • Maps to the most fitting portion Thursday, December 20, 12
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33. Questions? Thursday, December 20, 12
34. Sources • http://www.haskell.org/haskellwiki/Haskell • http://learnyouahaskell.com Thursday, December 20, 12