# Section of an infix operator

In Haskell there is a special syntax for partial application on infix operators. Essentially, you only give one of the arguments to the infix operator, and it represents a function which intuitively takes an argument and puts it on the "missing" side of the infix operator.

`(2^)`

(left section) is equivalent to`(^) 2`

, or more verbosely`\x -> 2 ^ x`

`(^2)`

(right section) is equivalent to`flip (^) 2`

, or more verbosely`\x -> x ^ 2`

Like partial application and lambda abstraction, sectioning provides a convenient way of writing some functions without having to explicitly name them:

`(1+)`

(unsugared:`(+) 1`

) is the "increment" function,`(2*)`

is the "double" function,`('\t':)`

is the "indent" function,`(`elem` "AEIOU")`

is the "is-capital-vowel-in-English" function (ignoring the "sometimes Y").

Note: as an exception, the "-" (subtraction) operator cannot do a right section, because that would be interpreted as unary negation in Haskell syntax. The Prelude function "subtract" is provided for this purpose. Instead of `(- e)`

, you need to write `(subtract e)`

.

Note: Iterated sections are also possible, as long the associativity is correct: `(1+2+)`

. The famous (but mostly useless) "Bender" operator is `(:8:[])`

.

## See also

- Currying
- Haskell report: Sections - see for more details