relude-0.2.0: Custom prelude from Kowainik

Copyright(c) 2016 Stephen Diehl
(c) 20016-2018 Serokell
(c) 2018 Kowainik
LicenseMIT
MaintainerKowainik <xrom.xkov@gmail.com>
Safe HaskellSafe
LanguageHaskell2010

Relude.Function

Description

This module reexports very basic and primitive functions and function combinators.

Synopsis
  • ($) :: (a -> b) -> a -> b
  • (&) :: a -> (a -> b) -> b
  • on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
  • fix :: (a -> a) -> a
  • flip :: (a -> b -> c) -> b -> a -> c
  • (.) :: (b -> c) -> (a -> b) -> a -> c
  • const :: a -> b -> a
  • id :: a -> a
  • identity :: a -> a

Documentation

($) :: (a -> b) -> a -> b infixr 0 #

Application operator. This operator is redundant, since ordinary application (f x) means the same as (f $ x). However, $ has low, right-associative binding precedence, so it sometimes allows parentheses to be omitted; for example:

f $ g $ h x  =  f (g (h x))

It is also useful in higher-order situations, such as map ($ 0) xs, or zipWith ($) fs xs.

(&) :: a -> (a -> b) -> b infixl 1 #

& is a reverse application operator. This provides notational convenience. Its precedence is one higher than that of the forward application operator $, which allows & to be nested in $.

>>> 5 & (+1) & show
"6"

Since: base-4.8.0.0

on :: (b -> b -> c) -> (a -> b) -> a -> a -> c infixl 0 #

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

fix f is the least fixed point of the function f, i.e. the least defined x such that f x = x.

For example, we can write the factorial function using direct recursion as

>>> let fac n = if n <= 1 then 1 else n * fac (n-1) in fac 5
120

This uses the fact that Haskell’s let introduces recursive bindings. We can rewrite this definition using fix,

>>> fix (\rec n -> if n <= 1 then 1 else n * rec (n-1)) 5
120

Instead of making a recursive call, we introduce a dummy parameter rec; when used within fix, this parameter then refers to fix' argument, hence the recursion is reintroduced.

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

flip f takes its (first) two arguments in the reverse order of f.

>>> flip (++) "hello" "world"
"worldhello"

(.) :: (b -> c) -> (a -> b) -> a -> c infixr 9 #

Function composition.

const :: a -> b -> a #

const x is a unary function which evaluates to x for all inputs.

>>> const 42 "hello"
42
>>> map (const 42) [0..3]
[42,42,42,42]

id :: a -> a #

Identity function.

id x = x

identity :: a -> a Source #

Renamed version of id.