Difference between revisions of "Cookbook/Lists"
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Furthermore, Haskell supports some neat concepts. |
Furthermore, Haskell supports some neat concepts. |
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− | =Infinite lists= |
+ | = Infinite lists = |
<haskell> |
<haskell> |
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Prelude> [1..] |
Prelude> [1..] |
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</haskell> |
</haskell> |
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− | =List comprehensions= |
+ | = List comprehensions = |
The list of all squares can also be written in a more comprehensive way, using list comprehensions: |
The list of all squares can also be written in a more comprehensive way, using list comprehensions: |
Revision as of 10:52, 23 April 2009
In Haskell, lists are what Arrays are in most other languages. Haskell has all of the general list manipulation functions, see also Data.List
.
head [1,2,3] --> 1
tail [1,2,3] --> [2,3]
length [1,2,3] --> 3
init [1,2,3] --> [1,2]
last [1,2,3] --> 3
Furthermore, Haskell supports some neat concepts.
Infinite lists
Prelude> [1..]
The list of all squares:
square x = x*x
squares = map square [1..]
But in the end, you probably don't want to use infinite lists, but make them finite. You can do this with take
:
Prelude> take 10 squares
[1,4,9,16,25,36,49,64,81,100]
List comprehensions
The list of all squares can also be written in a more comprehensive way, using list comprehensions:
squares = [x*x | x <- [1..]]
List comprehensions allow for constraints as well:
-- multiples of 3 or 5
mults = [ x | x <- [1..], mod x 3 == 0 || mod x 5 == 0 ]