postgrest/docs/Function.md

Functions

Composition

$

($) :: (a -> b) -> a -> b

Infix form of function application. Applies a function from a → b to an argument a.

Example:

> take 2 $ [1,2,3]
[1,2]

.

(.) :: (b -> c) -> (a -> b) -> a -> c

Function composition. Composes a function f (b → c) with a function g (a → b) yielding f ∘ g.

Example:

> map (negate . abs) [-1,0,1]  
[-1,0,-1]

&

(&) :: a -> (a -> b) -> b

Flipped form of ($) which applies an argument a to a function a → b.

Example:

> [1,2,3] & take 2
[1,2]

> replicate 10 3 & take 5 & tail
[3,3,3,3]

flip

flip :: (a -> b -> c) -> b -> a -> c

Flip takes a function of two arguments and returns a function taking the them in reverse order.

Example:

λ> flip take [1,2,3] 2
[1,2]

on

on :: (b -> b -> c) -> (a -> b) -> a -> a -> c

Example:

> sortBy (compare `on` fst) [(1,2), (3,4), (0,1)]
[(0,1),(1,2),(3,4)]

const

const :: a -> b -> a

Example:

fix

fix :: (a -> a) -> a

Example:

identity

identity :: a -> a

The identity function maps any value to itself.

applyN

Apply a function to a value n times.

Example:

applyN :: Int -> (a -> a) -> a -> a

> applyN 25 (+2) 0
50

> applyN 3 (1:) []
[1,1,1]

Strictness

$!

($!) :: NFData a => (a -> b) -> a -> b

Example:

$!!

($!!) :: NFData a => (a -> b) -> a -> b

Example:

force

force :: NFData a => a -> a

Example: