# Currying

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*<hask>("\t"++)</hask> is the "indent" function, | *<hask>("\t"++)</hask> is the "indent" function, | ||

*<hask>(`elem` "AEIOU")</hask> is the "is-capital-vowel-in-English" function (ignoring the "sometimes Y"). | *<hask>(`elem` "AEIOU")</hask> is the "is-capital-vowel-in-English" function (ignoring the "sometimes Y"). | ||

− | These are examples of [[partial application]] (and of | + | These are examples of [[partial application]] (and of a [[Section of an infix operator]]). |

Sometimes it's valuable to think about functions abstractly without specifically giving all their arguments: this is the [[Pointfree]] style. | Sometimes it's valuable to think about functions abstractly without specifically giving all their arguments: this is the [[Pointfree]] style. | ||

Sometimes half the work of the function can be done looking only at the first argument (but there really ''is'' only one argument, remember?): see [[functional dispatch]]. | Sometimes half the work of the function can be done looking only at the first argument (but there really ''is'' only one argument, remember?): see [[functional dispatch]]. |

## Revision as of 13:09, 31 May 2007

Currying is the process of transforming a function that takes multiple arguments into a function that takes just a single argument and returns another function if any arguments are still needed. In Haskell, *all* functions are considered curried: that is, *all functions in Haskell take just single arguments.*

div :: Int -> Int -> Int

div 11

*returns a function*of type

Int -> Int

Int -> Int -> Int

*really*saying is "takes an

Much of the time, currying can be ignored by the new programmer. The major advantage of considering all functions as curried is theoretical: formal proofs are easier when all functions are treated uniformly (one argument in, one result out). Having said that, there *are* Haskell idioms and techniques for which you need to understand currying.

Currying provides a convenient way of writing some functions without having to explicitly name them:

- (unsugared:(1+)) is the "increment" function,(+) 1
- is the "double" function,(2*)
- is the "indent" function,("\t"++)
- is the "is-capital-vowel-in-English" function (ignoring the "sometimes Y").(`elem` "AEIOU")

These are examples of partial application (and of a Section of an infix operator).

Sometimes it's valuable to think about functions abstractly without specifically giving all their arguments: this is the Pointfree style.

Sometimes half the work of the function can be done looking only at the first argument (but there really *is* only one argument, remember?): see functional dispatch.