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
15
votes
2 answers
Haskell: type inference and function composition
This question was inspired by this answer to another question, indicating that you can remove every occurrence of an element from a list using a function defined as:
removeall = filter . (/=)
Working it out with pencil and paper from the types of…
Pillsy
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14
votes
1 answer
Variadic compose function?
I'm trying to write a variadic function composition function. Which is basically the (.) except that the second argument function is variadic. This should allow expressions like:
map even . zipWith (+)
or just
map even . zipWith
Currently what…
is7s
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14
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compose function and functional module
Python 3.2 documentation refers to Collin Winter's functional module which contains function compose:
The compose() function implements function composition. In other
words, it returns a wrapper around the outer and inner callables, such
that…
max
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14
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Is there an operator for function composition in Julia?
Say I have two functions:
f(x) = x^2
g(x) = x + 2
Their composition is the function
h(x) = f(g(x))
Is there an operator for function composition in Julia? For example, if * was an operator for function composition (which it isn't), we could…
a06e
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13
votes
2 answers
Function composition in Haskell with tuple arguments
Sometimes I have two functions of the form:
f :: a -> (b1,b2)
h :: b1 -> b2 -> c
and I need the composition g. I solve this by changing h to h':
h' :: (b1,b2) -> c
Can you please show me (if possible) a function m, so that:
(h . m . f) == (h' .…
Jogusa
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13
votes
3 answers
Composing a Java Function and Consumer
What is the best way to functionally compose a java Function and a Consumer?
For example given some Function f and some Consumer c then doing f.andThen(c) would feel natural, however that is not how the interfaces work.
The…
kag0
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13
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3 answers
Functional composition with multi-valued functions in haskell?
I was wondering if it was possible to do functional composition with functions that take more than one argument. I want to be able to do something like this
x = (+3).(*)
setting x equal to a function that adds three to the product of two numbers.
MYV
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12
votes
2 answers
Expressing long chain of compositions in Haskell
(unimportant background info / motivation)
I was implementing a different version of nub, inspired by the Yesod book's discouragement of using it.
map head . group . sort is more efficient than a call to nub. However, in our case, order is…
Dan Burton
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12
votes
5 answers
How can I write a recursive compose function in R?
I would like to create a function, "compose" in R which will compose an arbitrary number of functions given as arguments.
So far, I have accomplished this by defining a function "of" that composes two arguments and then Reducing this:
of <-…
Alex Gian
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12
votes
3 answers
Is there a way to chain functions like withCString?
Is there a way to chain functions like withCString? By that I mean any
function that looks something like f :: Foo -> (CFoo -> IO a) -> IO a.
For example, lets say there is a function cFunc :: CString -> CFoo -> CBar -> IO ()
Usualy, I would do…
ivokosir
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11
votes
2 answers
Combining fragments of Haskell Code to get the bigger picture
This is the code that I came upon somewhere but want to know how this works:
findIndices :: (a -> Bool) -> [a] -> [Int]
findIndices _ [] = []
findIndices pred xs = map fst (filter (pred . snd) (zip [0..] xs))
Output: findIndices (== 0)…
user13231123
11
votes
5 answers
Composition of a hierarchy of functions
Is there a canonical way to express a function that is a composition of a rooted tree of functions?
Here is a concrete example of what I mean by "composition of a tree of functions." Take a rooted tree whose nodes are labelled by functions, like…
egnha
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11
votes
3 answers
Chaining methods left to right in Haskell (as opposed to right to left)
I come from Scala. So I frequently do stuff like:
println((1 to 10).filter(_ < 3).map(x => x*x))
In Haskell, after I discovered I can get rid of all the nested parenthesis using $ and ., I recently found myself writing:
putStrLn . show . map (**2)…
sscarduzio
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11
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1 answer
How Haskell's "composing lenses using function composition" with that weird order of arguments could be implemented?
I've been reading A wreq tutorial:
A lens provides a way to focus on a portion of a Haskell value. For
example, the Response type has a responseStatus lens, which
focuses on the status information returned by the server.
ghci> r ^.…
imz -- Ivan Zakharyaschev
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11
votes
4 answers
What is ((+) . (+)) in Haskell?
In ghci,
:t ((+).(+))
> ((+).(+)) :: (Num (a -> a), Num a) => a -> (a -> a) -> a -> a
but what is this thing? Can any one give me an example of the use of this please?
How can one composite 2 functions that take 2 parameters each?
for example, how…
Larry
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