Difference between revisions of "Cookbook/Lists"

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Furthermore, Haskell supports some neat concepts.
 
Furthermore, Haskell supports some neat concepts.
  
=Infinite lists=
+
= Infinite lists =
 
<haskell>
 
<haskell>
 
Prelude> [1..]
 
Prelude> [1..]
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</haskell>
 
</haskell>
  
=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 ]