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
8
votes
2 answers
How to compose a zero-argument function?
What I want to achieve is the 2 functions (one of them is no arg function) are composed into one.
Here is an example to give you idea what I am doing:
object Test extends App {
val zeroArgFunc = () => 10
val intArgFunc = (i: Int) => s"hello…
egordoe
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8
votes
5 answers
Expressive way compose generators in Python
I really like Python generators. In particular, I find that they are just the right tool for connecting to Rest endpoints - my client code only has to iterate on the generator that is connected the the endpoint. However, I am finding one area where…
chladni
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8
votes
2 answers
Why does my function composition implemented by reduce returns a closure?
I want to derive a composition function for n-functions from reduce/fold, but it doesn't work as expected:
$id = function ($x) {
return $x;
};
$comp = function ($f) {
return function ($g) use ($f) {
return function ($x) use ($f, $g) {
…
user6445533
8
votes
2 answers
Why is function composition in F# so much slower, by 60%, than piping?
Admittedly, I am unsure whether I am correctly comparing apples with apples or apples with pears here. But I'm particularly surprised about the bigness of the difference, where a slighter difference, if any, would be expected.
Piping can often be…
Abel
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8
votes
2 answers
Why does function composition compose from right to left in Javascript?
Function composition composes from right to left:
const comp = f => g => x => f(g(x));
const inc = x => x + 1;
const dec = x => x - 1;
const sqr = x => x * x;
let seq = comp(dec)(comp(sqr)(inc));
seq(2); // 8
seq(2) is transformed to…
user6445533
8
votes
2 answers
Haskell composition with two parameters
I'm trying to understand functional programming through Haskell and I'm having so much trouble dealing with function composition.
Actually I have these two functions :
add:: Integer -> Integer -> Integer
add x y = x + y
sub:: Integer -> Integer ->…
Thomas thomas
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8
votes
1 answer
Why does the dot compose from right to left in Haskell?
If we have two functions, f and g, then in Haskell h = f . g is equivalent to h x = f(g x). I.e. the functions are applied from right to left to the input. Is there any fundamental reason why it goes from right to left, and not from left to right?…
Tiddo
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8
votes
2 answers
Difference between function composition operator (.) and fmap (<$>)
Currently reading through this article (which is pretty brilliant btw) and have a pretty simple question:
If I combine two functions like (+3) and (+2) with <$>, it seems to give me a new function that adds 5 to whatever is passed to it. If I do the…
Brendan
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8
votes
2 answers
Haskell notation for composing two functions f and g where g takes multiple arguments
Often I find I want to compose two functions f and g, but g takes multiple arguments. Does Haskell provide a set of operators for that (I know I could write it myself, but it seems fairly common and I don't want to duplicate an operator that…
dspyz
- 5,280
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8
votes
2 answers
Haskell: Why is ((.).(.)) f g equal to f . g x?
Could you please explain the meaning of the expression ((.).(.))?
As far as I know (.) has the type (b -> c) -> (a -> b) -> a -> c.
user2043097
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- 1
8
votes
3 answers
foldl . foldr function composition - Haskell
So, I'm really frying my brain trying do understand the foldl.foldr composition.
Here is a example:
(foldl.foldr) (+) 1 [[1,2,3],[4,5,6]]
The result is 22, but what's really happening here?
To me it looks like this is what is happening: foldl (+) 1…
dehq
- 449
- 5
- 12
8
votes
2 answers
efficient list append/prepend through function composition
Some months ago I read somewhere of an efficient approach for appending and prepending lists to other lists in O(1) by representing them with function compositions that, once evaluated, build in O(n) the resulting list.
Unfortunately I cannot…
Riccardo T.
- 8,907
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7
votes
1 answer
Haskell: difference in performance from different function composition?
The following code:
import Control.Exception
import Data.List
updateAverage :: (Fractional t) => (t, t) -> t -> (t, t)
updateAverage (old_value, old_counter) x =
let new_counter = old_counter + 1
in
assert(new_counter /= 0)
…
quant_dev
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7
votes
1 answer
(How) Can you curry compose monadic functions?
I have the following functions:
f: a -> m[b]
g: (b,c) -> m[d]
h: (a,c) -> m[d]
How can h be expressed as a composition of f and g?
Using do/for notation we can implement h easily like so:
h: (a,c) => {
for {
b <- f(a)
d <- g(b,c)
} yield…
PhD
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7
votes
3 answers
A function composition operator in Python
In this question I asked about a function composition operator in Python. @Philip Tzou offered the following code, which does the job.
import functools
class Composable:
def __init__(self, func):
self.func = func
…
RussAbbott
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