Difference between revisions of "Cookbook/Lists"
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| − | In Haskell, lists are what Arrays are in most other languages. Haskell has all of the general list manipulation functions, see also <hask>Data.List</hask>. |
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| − | <haskell> |
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| − | head [1,2,3] --> 1 |
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| − | tail [1,2,3] --> [2,3] |
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| − | length [1,2,3] --> 3 |
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| − | init [1,2,3] --> [1,2] |
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| − | last [1,2,3] --> 3 |
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| − | </haskell> |
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| − | Furthermore, Haskell supports some neat concepts. |
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| − | = Infinite lists = |
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| − | <haskell> |
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| − | Prelude> [1..] |
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| − | </haskell> |
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| − | The list of all squares: |
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| − | <haskell> |
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| − | square x = x*x |
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| − | squares = map square [1..] |
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| − | </haskell> |
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| − | But in the end, you probably don't want to use infinite lists, but make them finite. You can do this with <hask>take</hask>: |
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| − | <haskell> |
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| − | Prelude> take 10 squares |
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| − | [1,4,9,16,25,36,49,64,81,100] |
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| − | </haskell> |
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| − | = List comprehensions = |
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| − | The list of all squares can also be written in a more comprehensive way, using list comprehensions: |
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| − | <haskell> |
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| − | squares = [x*x | x <- [1..]] |
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| − | </haskell> |
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| − | List comprehensions allow for constraints as well: |
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| − | <haskell> |
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| − | -- multiples of 3 or 5 |
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| − | mults = [ x | x <- [1..], mod x 3 == 0 || mod x 5 == 0 ] |
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| − | </haskell> |
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