Applying one function to the result of another is known as function composition: `(f.g)(x) = f(g(x))`
Applying one function to the result of another is known as function composition: (f.g)(x) = f(g(x)).
See also pointfree.
Questions tagged [function-composition]
420 questions
0
votes
2 answers
JS functions composed in the opposite order
Starting with a simple function composition
const fa = (x => (x + "a"));
const fb = (x => (x + "b"));
fb(fa('x'))
I played around and I obtained the following code snippet which returns 'xba' instead of 'xab'.
Can someone explain why?
const fa =…
Tres
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Creating function: (f, n) which return f(f(f( .... x... ))) n times
I am having trouble creating a higher order function in python that applies a function f, n times to generate a new function h, as its return value.
def compile(f, n)
# h is a function, f applied n times
...
return h
new =…
user9873466
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0 answers
How to calculate a composite function on the grid?
I have two random variables, x is beta-distributed on the interval [2, 6] and y is uniformly distributed on the interval [0, 1]. For every x I would like to find y such that CDF_x(x) = CDF_x(y) and plot the graph. In other words I would like to get…
Anna Ignashkina
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2 answers
How to compose functions like zip-apply-ish
Assuming I have a bunch of functions of arity 2: f: a b -> x, g: c d -> y,
etc. up to unary function u: a -> a. What I would like to do is to chain them in such a way:
f(_, g(_, .... z(_, u(_))...)
where inside _ placeholders consecutive values…
SOReader
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votes
1 answer
Use composed map in AutoMapper
Suppose my AutoMapper configuration knows how to map from type T1 to type T2 and from T2 to type T3. I then have the following. It works:
public static class MapperExtensions
{
public static T3 MapVia(this IMapper mapper, T1 t1) {
…
WhatGoodIsAName
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0
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2 answers
sicp 1.44 why it is a #
#lang planet neil/sicp
(define dx 0.00001)
(define (smooth-n f n)
(repeat smooth f n))
(define (smooth f)
(lambda (x) (/ (+ (f x) (f (- x dx)) (f (+ x dx))) 3)))
(define (compose f g)
(lambda (x) (f (g x))))
(define (repeat f g n)
…
song qi
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0
votes
1 answer
Haskell: a case of composition
This is a useless case of concatenation via foldl, purely educational (for me):
foldl (\xs x -> xs ++ [x]) [1,2] [11,12,13]
[1,2,11,12,13]
Is there a way to pack it even tighter, using composition instead of the lambda?
Alexey Orlov
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0
votes
1 answer
TypeScript class A's method to work as a pass-through to a B's method
I am trying to wrap a third-party library auth0-js into my own class. In the example below an Authentication class from Auth0.js is being wrapped and is used as the implementation for the pass-through methods. See how buildLogoutUrl(options) does…
Igor Soloydenko
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0
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2 answers
Type of (map . map)
I'm trying to understand the type of the expression (map . map). Since the type of (.) is (b -> c) -> (a -> b) -> a -> c I don't understand how this works with the map function, because map takes two arguments which doesn't fit with the functions (b…
Nicrophorus
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0
votes
1 answer
Writing length foldr with function composition
I would like to rewrite
foldr (\_ y = y + 1) 0
using flip, const and (+1) and function composition.
I've gotten this far:
foldr (\x -> ((+1) . (flip const x)) 0
But I can't seem to ditch this lambda. Is there any way to do so?
hgiesel
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0
votes
1 answer
SML: Function composition with isSome
I have the following examples and they do not work even though the types do matchup with each other
- isSome;
val it = fn : 'a option -> bool
- SOME;
val it = fn : 'a -> 'a option
- val my_converter = (fn x => if x = 5 then SOME x else NONE);
val…
Har
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0
votes
1 answer
Composing functions 'length' and 'elemIndices'
I wrote a function count :: Char -> String -> Int that counts the number of occurrences of a Char inside a String. Code sample:
module Main where
import Data.List
main :: IO ()
main = do
print $ count 'a' "abcaaba"
count :: Char -> String…
TobiMcNamobi
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0
votes
1 answer
Please explain how the compose function in redux works
The compose function in Redux is really simple for the most part and I understand how to use it.
export default function compose(...funcs) {
if (funcs.length === 0) {
return arg => arg
}
if (funcs.length === 1) {
return funcs[0]
…
Amit Erandole
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0
votes
3 answers
Monadic Function composition with chaining in Java 8
Somehow I should be able to specify a chain like this while value is piped through each function.
a::create -> a::processing -> a::updating -> a:uploading
In context of following articles I want to chain the methods with one method passing the…
user2727195
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0
votes
1 answer
Function composition in Scheme
I'm trying to modify the function below to compose two functions in Scheme.
(define (compose F1 F2)
(eval F1 (interaction-environment))
)
rather than
(define (compose f g)
(λ (x) (f (g x))))
But I'm not sure about how to use eval.
Morovo
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