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
11
votes
7 answers
Better Function Composition in Python
I work in Python. Recently, I discovered a wonderful little package called fn. I've been using it for function composition.
For example, instead of:
baz(bar(foo(x))))
with fn, you can write:
(F() >> foo >> bar >> baz)(x) .
When I saw this, I…
Charles R
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10
votes
3 answers
What am I missing: is function composition with multiple arguments possible?
I understand the basics of function composition in F#, as, for example, described here.
Maybe I am missing something, though. The >> and << operators seem to have been defined with the assumption that each function only takes one argument:
>…
Kevin Cantu
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10
votes
1 answer
Typescript recursive function composition
I want to create a function chain, which would be an input of a pipe/flow/compose function.
Is this possible without the literal expansion of the types to selected depth, as is this usually handled? See lodash's flow.
I want to achieve typecheck of…
Jaroslav Šmolík
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10
votes
2 answers
Why does function composition require parentheses?
Let's say I want to compose Text.pack with Text.strip.
:t (.) produces: (b -> c) -> (a -> b) -> a -> c
:t (Text.pack) produces: String -> Text
:t (Text.strip) produces: Text -> Text
So substituting strip for (b -> c) gives:
b = Text
c =…
Abraham P
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9
votes
2 answers
Haskell Rewrite Rules and Function Composition
Why does haskell require multiple rewrite rules depending on the function composition technique and length? Is there a way to avoid this?
For example, given the following code...
{-# RULES
"f/f" forall a. f ( f a ) = 4*a
#-}
f a = 2 * a
this…
Toymakerii
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9
votes
6 answers
Pointfree function combination in Python
I have some predicates, e.g.:
is_divisible_by_13 = lambda i: i % 13 == 0
is_palindrome = lambda x: str(x) == str(x)[::-1]
and want to logically combine them as in:
filter(lambda x: is_divisible_by_13(x) and is_palindrome(x), range(1000,10000))
The…
Frank S. Thomas
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9
votes
5 answers
composition with dyadic operator?
I want to do something fairly simple;
I am using the operator (++) with Data.Map insertWith, and it works fine, but I want to eliminate duplicates in the value created, so want to compose it with nub.
I tried (nub (++)), (nub $ (++)), (nub . (++)),…
guthrie
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9
votes
2 answers
Haskell - How does this average function work?
I found this implementation of the average function:
avg :: [Int] -> Int
avg = div . sum <*> length
How does this work? I looked at the function that was produced as a result of div . sum:
(div . sum) :: (Integral a, Foldable t) => t a -> a -> a
I…
xilpex
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9
votes
3 answers
Composite functions in ocaml
How can I define a composite function in a functional language, in particular with Ocaml? For example, if I write a function that calculates the negation of the result of another function, that is: not(f(x)) where f(x) returns a boolean. How can I…
kafka
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9
votes
2 answers
Railway oriented programming with Async operations
Previously asked similar question but somehow I'm not finding my way out, attempting again with another example.
The code as a starting point (a bit trimmed) is available at https://ideone.com/zkQcIU.
(it has some issue recognizing…
Developer11
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9
votes
1 answer
Serialize Composed Func?
This works fine:
Func func1 = s => s + "func";
ViewState["function"] = func1;
However, this does not:
Func func1 = s => s + "func";
Func func2 = s => func1(s);
…
Fishtoaster
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9
votes
1 answer
Python function composition
I've tried to implement function composition with nice syntax and here is what I've got:
from functools import partial
class _compfunc(partial):
def __lshift__(self, y):
f = lambda *args, **kwargs: self.func(y(*args, **kwargs))
…
si14
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9
votes
5 answers
Composing functions in Java?
I'm writing demo code for an API we've created and I keep running into the same problem where I'm repeating myself, over and over ad nauseum. I am painfully aware that Java is scheduled to have closures added but I don't have access to them now. …
wheaties
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9
votes
4 answers
How to combine two procs into one?
Just wondering if there's a syntax shortcut for taking two procs and joining them so that output of one is passed to the other, equivalent to:
a = ->(x) { x + 1 }
b = ->(x) { x * 10 }
c = ->(x) { b.( a.( x ) ) }
This would come in handy when…
Gunchars
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8
votes
2 answers
Composing a chain of 2-argument functions
So I have a list of a functions of two arguments of the type [a -> a -> a]
I want to write a function which will take the list and compose them into a chain of functions which takes length+1 arguments composed on the left. For example if I have…
Stephen Diehl
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