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
4 answers
Use tail recursion to achieve repeated function composition
I need to define a function (repeat-write n f) so that
((repeat-write n f) x) evaluates to (f (f (... (f x) ...)))
where there are n applications of the function f.
For example:
((repeat-write 4 cdr) ’(1 2 3 4 5 6))
evaluates to
’(5 6)
I'm not too…
Varun Vijayan
- 25
- 3
0
votes
2 answers
Failing composition of functorial and monadic operations
Another newbie question in my struggle to learn idiomatic Haskell: I'm trying to compose a smart constructor out of some validation functions, but I can't get the types to line up.
This is the type I want to construct:
newtype Tag = Tag { getTag ::…
Ulrich Schuster
- 1,670
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votes
1 answer
JavaScript bind sets the second argument equal to the first one when it should be undefined?
I recently tried to understand function composition in javascript. I understood what currying is and how it works, but I saw this code and I can't really understand it. It's function composition using .reduce(...). This is the code:
const compose =…
David
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votes
1 answer
Use compose with several functions and inner function with param
I have the following:
{
reseller: filterOutNonUsable(dedupe(extractArrVals(data.locks.entries, 'reseller')))
}
What is the best way to call all these functions and use a second parameter for the extractArrVals function (see my example) so…
Gutelaunetyp
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votes
5 answers
Combine 2 list functions into 1?
How would I combine the following 2 functions:
replaceNth n newVal (x:xs)
| n == 0 = newVal:xs
| otherwise = x:replaceNth (n-1) newVal xs
replaceMthNth m n v arg = replaceNth m (replaceNth n v (arg !! m)) arg
into a single function?
Is it…
maclunian
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votes
0 answers
Is there a more concise way to define this array of function values in Python?
I am new to Python. I want to apply various permutations of three functions f, g, and h where juxtaposition means function composition (e.g., fg(x) = f(g(x))) to say, a list x of boolean integers, and put the results in an array. To make it easy…
mathematrucker
- 166
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- 9
0
votes
1 answer
Compose lambda function in C++ using parameter pack
I'm new to C++ 14, I want to compose a variable length of lambda functions together to a single lambda, how should I do that? Below is my current work
#include
template
Ftype compose(const Ftype & fn) {
return…
user7804610
- 9
- 3
0
votes
1 answer
Error in using composed function in further function composition
I am having trouble understanding why I am unable to use a composed function and compose a new one. For eg: I have two functions f and g and I create a composed function composed1 from these. I tried to combine composed with fourth function lastOne…
Aandal
- 51
- 2
- 11
0
votes
1 answer
How to use intermediate results in vertx future compose?
I am chaining some calls and I need to use the outcome of 1 future in a following call.
In the example below, what would be the most elegant way to be able to use res1?
call1()
.compose(res1 -> call2(res1))
.compose(res2 ->…
Orkun
- 6,998
- 8
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0
votes
2 answers
Haskell - fast naming of projection functions
Suppose I want to define a function f in terms of some other predefined function g as follows:
f :: Int -> Int -> Int
f 2 b = g b
f _ _ = 1
That is, I want to define the projection, f(2,_) : Int->Int to be the same as g(_) : Int->Int. Gladly,…
Owen
- 448
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- 11
0
votes
3 answers
Ramda: Confused about pipe
I'm learning functional programming in JS and I'm doing it with Ramda.
I'm trying to make a function that takes parameters and returns a list. Here is the code:
const list = R.unapply(R.identity);
list(1, 2, 3); // => [1, 2, 3]
Now I tried doing…
J. Hesters
- 13,117
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- 249
0
votes
1 answer
What is the type of this haskell double function composition?
t2 = (\x y z-> x.y.x)
GHCI shows me this:
t2 :: (b1 -> b2) -> (b2 -> b1) -> p -> b1 -> b2
I can't quite grasp it how this type signature comes to be. So far I've figured that the righter-most x is basically a function which takes a b2 and returns a…
Minimax
- 121
- 1
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0
votes
1 answer
Validate input with any function in a list
Say I want to validate an input that has to satisfy one of a number of functions. What is the best way to do this in F#? Here’s a little example I came up with.
let funcs =
[
fun x -> x % 2 = 0
fun x ->…
Brett Rowberry
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0
votes
1 answer
Can I use the same function names when using Object.assign() in composition?
Context
I created a new object using a composition paradigm in Javascript.
const canUpdateScore = (state) => ({
update: (spell) => state.score--
})
const mage = (name) => {
let state = {
score: 100,
}
return Object.assign(state,…
Jason Allshorn
- 1,625
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0
votes
1 answer
Function Composition Error
While going through a tutorial on Function Composition, I tried the following:
let prefixFun a b = a + "" + b;;
let exclaim s = s + "!";;
let bigHello = prefixFun >> exclaim;;
But the definition for bigHello returns the following type mismatch…
Yelena
- 423
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