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List comprehension
A list comprehension is a Haskell syntax that is similar to "set comprehensions" or "set-builder notation", ie the notation
In Haskell list comprehensions this would be written as
S = [ x | x<-[0..], x^2>3]
where [0..] represents N, and x^2>3 represents the conditional. It is clear that the two notations are almost identical.
The Haskell interpreter actually converts instances of list comprehensions to expressions involving the higher-order functions map and filter.
For example S above can be written as
S = filter (\x -> x^2 > 3) [0..]
The Python programming language has a near-equivalent mechanism for expressing list comprehensions. Corresponding example would be:
L = range(100) # this produces a list of integers from 0 to 99 S = [x for x in L if x**2 > 3]
Last updated: 08-07-2005 17:07:12
09-23-2007 01:00:40
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The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details