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 purely functional, lazy, 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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− | |||
− | == Basics == |
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− | {| class="wikitable" |
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− | |- |
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− | ! Question |
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− | ! Answer |
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− | |- |
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− | |What is an '''infix operator'''? |
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− | | Infix operators are normal functions. TODO: symbols, round brackets |
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− | For example: |
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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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− | |- |
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− | |How do you '''define a function''' in Haskell? |
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− | | TODO |
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− | For example: |
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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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− | |- |
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− | |What is '''point-free style'''? |
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− | |Point-free style is a way to define functions solely as a composition of other functions, leaving out arguments in the definition. |
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− | For example: |
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− | <haskell>takeFive x = take 5 x</haskell> |
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− | is the same as |
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− | <haskell>takeFive = take 5</haskell> |
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− | in point-free style. |
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− | |- |
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− | |What is '''currying'''? |
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− | | TODO |
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− | |- |
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− | |What is '''pattern matching'''? |
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− | | TODO |
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− | |||
− | |} |
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− | |||
− | == Advanced == |
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− | |||
− | {| class="wikitable" |
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− | |- |
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− | ! Question |
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− | ! Answer |
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− | |- |
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− | |What is a '''Monad'''? |
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− | |TODO |
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− | |- |
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− | |What is the meaning of "'''forall'''"? |
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− | |TODO |
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− | |} |
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− | |||
− | == Special characters, expressions and keywords == |
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− | |||
− | === . === |
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− | The dot "." is used to compose functions in point-free style, similar to "$". |
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− | |||
− | Example: |
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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 = h . g . f</haskell> |
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− | |||
− | === ` === |
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− | A function enclosed in back ticks "`"s can be used as an infix operator. |
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− | |||
− | Example: |
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− | <haskell>subtract 2 10</haskell> |
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− | is the same as |
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− | <haskell>2 `subtract` 10</haskell> |
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− | |||
− | === ' === |
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− | Backtick TODO: single characters, common usage in function names |
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− | |||
− | === : === |
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− | The colon ":" is an infix operator that adds an element to the beginning of a list |
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− | |||
− | Example: |
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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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− | The double colon TODO |
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− | |||
− | === | === |
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− | Downslash TODO: pattern matching, data types |
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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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− | The dollar sign "$" is a way to compose functions, but avoid typing too many brackets. |
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− | |||
− | Example: |
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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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− | The double dash "-- " (a trailing space is necessary) begins a '''single-line comment'''. The rest of the line will be ignored by the compiler. |
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− | |||
− | Example: |
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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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− | 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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− | ! Examples |
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− | |- |
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− | |Everything between "{- " and "-}" is a '''block comment''' and will be ignored by the compiler. |
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− | |||
− | Note that the space after "{- " is necessary. |
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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>{- Block quotes can also be used for single line comments -}</haskell> |
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− | |} |
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− | |||
− | === {-# #-} === |
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− | "{-# " (the trailing space is necessay) and "#-}" define '''compiler pragmas'''. TODO |
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− | |||
− | === data === |
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− | "data" defines a new data type. TODO |
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− | |||
− | Example: |
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− | <haskell>data colors = Red | Blue | Green</haskell> |
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− | |||
− | === deriving === |
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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 |