User:Lenny222/Haskell explained to the busy

You have heard about Haskell but don't have the time to find out what it is?

This page may be for you.

Introduction

What is Haskell?

Haskell is a purely functional, lazy, statically typed programming language

What is a purely functional programming language?

What is good about that?

What is lazy evaluation?

What is good about that?

What is static typing?

What is good about that?

Why the name "Haskell"?

Haskell is named after the American mathematician Haskell Curry

Functions

How do i apply functions?

TODO

What is partial application?

Answer	Example
By passing less than the full set of arguments to a function that takes multiple arguments, one can create new functions.	add :: Int -> Int -> Int add x y = x + y addOne = add 1

What is the "Prelude"?

The Prelude is a standard module that is available to all Haskell code by default.

What is currying?

TODO

How do i define a function?

Answer	Example
TODO	add x y = x + y

Didn't you say Haskell is statically typed? It is. TODO

What is an infix operator?

Answer	Example
Infix operators are normal functions. TODO: symbols, round brackets	5 + 2 is the same as (+) 5 2

Are there any prefix operators?

TODO: (-)

What is point-free style?

Answer	Example
Point-free style is a way to define functions solely as a composition of other functions. Function arguments do not show up in the function definition.	The point-free style version of takeFive x = take 5 x is takeFive = take 5

What is a higher-order function?

TODO

What is pattern matching?

TODO

Data types

TODO

Lists

TODO

Strings

TODO

Tupels

TODO

Type classes

What is a type variable?

TODO

What is a type class?

TODO

Comments

How do i write single-line comments?

Answer	Example
Everything between a double dash "--" followed by a space and the end of the line is a single-line comment. A single-line comment will be ignored by the compiler.	-- Sort the list sort [3,2,4] or sort [3,2,4] -- Sort the list

How do i write block comments?

Answer	Examples
Everything between "{-" followed by a space and "-}" is a block comment. A block comment will be ignored by the compiler.	{- The next line would sort the list, if it wasn't in a block comment sort [3,2,4] -} or sort [3,2,4] {- Block quotes can also be used for single line comments -}

Special characters, expressions and keywords

.

Meaning	Example
The dot "." is used to compose functions in point-free style, similar to "$".	foo = h . g . f is the same as foo x = h $ g $ f x which is the same as foo x = h (g (f x))

`

Meaning	Example
A function enclosed in back ticks "`" can be used as an infix operator.	2 `subtract` 10 is the same as subtract 2 10

'

Tick TODO: single characters, common usage in function names

:

Meaning	Example
The colon ":" is an infix operator that adds an element to the beginning of a list.	1 : [2,3] will result in the new list [1,2,3]

::

The double colon TODO

|

Downslash TODO: pattern matching, data types

\

Backslash TODO: multiline strings, lambda function

$

Meaning	Example
The dollar sign "$" is a way to compose functions, without typing too many brackets.	foo x = h $ g $ f x is the same as foo x = h (g (f x))

@

TODO: as-pattern

--

Meaning	Example
The double dash "--" followed by a space begins a single-line comment.	-- A single-line comment

[ ]

The square brackets TODO

{- -}

Meaning	Example
Everything between "{-" followed by a space and "-}" is a block comment.	{- This is a block comment -}

{-# #-}

Meaning	Example
Everything between "{-#" followed by a space and "#-}" defines a compiler pragma.	{-# INCLUDE "foo.h" #-}

data

Meaning	Example
"data" defines a new data type. TODO	data colors = Red | Blue | Green

deriving

TODO

forall

TODO

newtype

TODO

type

TODO