Difference between revisions of "User:Lenny222/Haskell explained to the busy"
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| − | You have heard about Haskell but don't have the time to find out what it is? |
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| − | |||
| − | This page may be for you. |
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| − | |||
| − | == Introduction == |
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| − | |||
| − | === What is Haskell? === |
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| − | Haskell is a [[#What is a purely functional programming language?|purely functional]], [[#What is lazy evaluation?|lazy]], [[#What is static typing?|statically typed]] programming language |
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| − | |||
| − | === What is a purely functional programming language? === |
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| − | What is good about that? |
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| − | |||
| − | === What is lazy evaluation? === |
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| − | What is good about that? |
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| − | |||
| − | === What is static typing? === |
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| − | What is good about that? |
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| − | |||
| − | === Is Haskell '''Open Source'''? === |
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| − | === Why the name '''"Haskell"'''? === |
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| − | Haskell is named after the American mathematician [http://en.wikipedia.org/wiki/Haskell_Curry Haskell Curry] |
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| − | |||
| − | == Functions == |
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| − | |||
| − | === How do i apply functions? === |
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| − | TODO |
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| − | |||
| − | === What is partial application? === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Answer |
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| − | ! Example |
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| − | |- |
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| − | |By passing less than the full set of arguments to a function, one can create new functions. |
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| − | |With the function |
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| − | <haskell> |
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| − | add :: Int -> Int -> Int |
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| − | add x y = x + y |
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| − | </haskell> |
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| − | that adds two numbers, we can define another function |
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| − | <haskell> |
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| − | addOne = add 1 |
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| − | </haskell> |
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| − | that adds 1 to any given number. |
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| − | |} |
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| − | |||
| − | === What is the "Prelude"? === |
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| − | |||
| − | The Prelude is a standard module that is available to all Haskell code by default. |
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| − | |||
| − | === What is currying? === |
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| − | TODO |
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| − | |||
| − | === How do i define a function? === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Answer |
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| − | ! Example |
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| − | |- |
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| − | |TODO |
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| − | |<haskell>add x y = x + y</haskell> |
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| − | |} |
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| − | |||
| − | Didn't you say Haskell is statically typed? |
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| − | It is. TODO |
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| − | |||
| − | === What is an infix operator? === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Answer |
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| − | ! Example |
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| − | |- |
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| − | |Infix operators are normal functions. |
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| − | |||
| − | TODO: symbols, round brackets |
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| − | |<haskell>5 + 2</haskell> |
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| − | is the same as |
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| − | <haskell>(+) 5 2</haskell> |
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| − | |} |
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| − | |||
| − | |||
| − | === Are there any prefix operators? === |
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| − | |||
| − | TODO: (-) |
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| − | |||
| − | === What is point-free style? === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Answer |
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| − | ! Example |
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| − | |- |
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| − | |Point-free style is a way to define functions solely as a composition of other functions. |
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| − | Function arguments do not show up in the function definition. |
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| − | |The point-free style version of |
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| − | <haskell>takeFive x = take 5 x</haskell> |
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| − | is |
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| − | <haskell>takeFive = take 5</haskell> |
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| − | |} |
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| − | |||
| − | === What is a higher-order function? === |
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| − | TODO |
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| − | |||
| − | === What is pattern matching? === |
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| − | TODO |
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| − | |||
| − | == Data types == |
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| − | TODO |
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| − | |||
| − | === Lists === |
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| − | TODO |
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| − | |||
| − | === Strings === |
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| − | TODO |
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| − | |||
| − | === Tupels === |
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| − | TODO |
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| − | |||
| − | === Tuples === |
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| − | |||
| − | === Defining your own types === |
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| − | |||
| − | == Type classes == |
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| − | |||
| − | === What is a type variable? === |
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| − | TODO |
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| − | |||
| − | === What is a type class? === |
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| − | TODO |
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| − | |||
| − | == Comments == |
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| − | |||
| − | === How do one write single-line comments? === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Answer |
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| − | ! Example |
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| − | |- |
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| − | |Everything between a double dash "'''--'''" followed by a '''space''' and the end of the line is a single-line comment. |
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| − | A single-line comment will be ignored by the compiler. |
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| − | |<haskell>-- Sort the list |
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| − | sort [3,2,4] |
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| − | </haskell> |
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| − | or |
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| − | <haskell>sort [3,2,4] -- Sort the list</haskell> |
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| − | |} |
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| − | |||
| − | === How do one write block comments? === |
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| − | {| class="wikitable" |
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| − | |- |
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| − | ! Answer |
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| − | ! Examples |
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| − | |- |
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| − | |Everything between "'''{-'''" followed by a '''space''' and "'''-}'''" is a block comment. |
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| − | A block comment will be ignored by the compiler. |
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| − | |<haskell> |
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| − | {- |
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| − | The next line would sort the list, if it wasn't in a block comment |
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| − | sort [3,2,4] |
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| − | -} |
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| − | </haskell> |
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| − | or |
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| − | <haskell>sort [3,2,4] {- Block quotes can also be used for single line comments -}</haskell> |
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| − | |} |
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| − | |||
| − | == Special characters, expressions and keywords == |
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| − | |||
| − | === . === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |The dot "." is used to compose functions in [[#What is point-free style? |point-free style]], similar to "[[#$|$]]". |
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| − | |<haskell>foo = h . g . f</haskell> |
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| − | is the same as |
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| − | <haskell>foo x = h $ g $ f x</haskell> |
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| − | which is the same as |
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| − | <haskell>foo x = h (g (f x))</haskell> |
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| − | |} |
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| − | |||
| − | === ` === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |A function enclosed in back ticks "`" can be used as an [[#What is an infix operator?|infix operator]]. |
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| − | |<haskell>2 `subtract` 10</haskell> |
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| − | is the same as |
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| − | <haskell>subtract 2 10</haskell> |
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| − | |} |
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| − | |||
| − | === ' === |
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| − | Tick TODO: single characters, common usage in function names |
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| − | |||
| − | === : === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |The colon ":" is an [[#What is an infix operator?|infix operator]] that adds an element to the beginning of a list. |
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| − | |<haskell>1 : [2,3]</haskell> |
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| − | will result in the new list |
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| − | <haskell>[1,2,3]</haskell> |
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| − | |} |
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| − | |||
| − | === :: === |
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| − | The double colon TODO |
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| − | |||
| − | === | === |
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| − | Downslash TODO: pattern matching, data types, Functional dependencies |
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| − | |||
| − | === \ === |
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| − | Backslash |
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| − | TODO: multiline strings, lambda function |
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| − | |||
| − | === $ === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |The dollar sign "$" is a way to compose functions, without typing too many brackets. |
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| − | |<haskell>foo x = h $ g $ f x</haskell> |
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| − | is the same as |
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| − | <haskell>foo x = h (g (f x))</haskell> |
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| − | |} |
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| − | |||
| − | === @ === |
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| − | TODO: as-pattern |
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| − | |||
| − | === -- === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |The double dash "--" followed by a space begins a [[#How do one write single-line comments?|single-line comment]]. |
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| − | |<haskell>-- A single-line comment</haskell> |
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| − | |} |
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| − | |||
| − | === [ ] === |
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| − | The square brackets TODO |
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| − | |||
| − | === {- -} === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |Everything between "{-" followed by a space and "-}" is a [[#How do one write block comments?|block comment]]. |
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| − | |<haskell>{- |
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| − | This is a block comment |
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| − | -}</haskell> |
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| − | |} |
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| − | |||
| − | === {-# #-} === |
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| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | |Everything between "{-#" followed by a space and "#-}" defines a compiler pragma. |
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| − | |<haskell> |
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| − | {-# INCLUDE "foo.h" #-} |
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| − | </haskell> |
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| − | |} |
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| − | |||
| − | === data === |
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| − | |||
| − | {| class="wikitable" |
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| − | |- |
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| − | ! Meaning |
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| − | ! Example |
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| − | |- |
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| − | | |
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| − | "data" defines a new data type. TODO |
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| − | | |
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| − | <haskell>data colors = Red | Blue | Green</haskell> |
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| − | |} |
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| − | |||
| − | === deriving === |
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| − | TODO |
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| − | |||
| − | === forall === |
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| − | TODO |
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| − | |||
| − | === newtype === |
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| − | TODO |
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| − | |||
| − | === type === |
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| − | TODO |
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