Haskell
Chris Bentivenga
http://sse.se.rit.edu/go/haskell_talk
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Go To:
http://sse.se.rit.edu/go/haskell_talk
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What is Haskell?
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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
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Polymorphically
Statically Typed
•id :: a -> a
•Char -> Char
• Int -> Int
• Bool -> Bool
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Lazy
• Not evaluated when bound
• Evaluated when executed
• take 5 [1..]
• [1,2,3,4,5]
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Purely Functional
• Imperative (OO, Procedural):
• Execute statements
• Change state
• Functional:
• Evaluate expressions
• No state
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Features of Functional
Languages
• High Order Functions
• Purity
• Lazy Execution
• Recursion
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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]
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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
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Lazy
• Not evaluated when bound
• Evaluated when executed
• take 5 [1..]
• [1,2,3,4,5]
Already Saw This!
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Recursion
• Same as recursion in any other paradigim
• One of the few ways to iterate
• Is no for loop
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Getting Started in
Haskell
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Haskell Basics
• Entry point: main function (like C, C++)
• Basic output function: print
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Haskell Functions
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Silly Silly Haskell
Notation
• $ -- Function Applicator
• . -- Function Composition
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Currying
• Partially fill out the parameters on a
function
• Creates a new function that expects fewer
paramaters
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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...
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Typing System
• Strictly typed under the hood
• Don’t have to see those types
• Can explicitly write out types on a function
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/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"
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Lists
• Standard functional data structure
• List operations: map, filter, reduce, etc...
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Pattern Matching
• Function headers have portions already
declared
• Maps to the most fitting portion
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Questions?
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Sources
• http://www.haskell.org/haskellwiki/Haskell
• http://learnyouahaskell.com
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