CODEWITHSUNDEEP
javascriptfunctional-programmingramda.js
Sam Pettersson
Sam Pettersson

Reputation: 3227

Is there a name for this function

I am looking for a name for the following function:

(f, a) => () => f(a)

Basically a function that returns a function which when called calls f with a.

Is there a common name for this function? maybe it can be described with some Ramda magic?

Edit to clarify:

What I'm looking for is similar to Ramda's partial,

partial(f, [a])

Except that partial is more like:

(f, a) => (b) => f(a, b)

I.e the b in the case of partial is unwanted.

Upvotes: 4

Views: 411

Answers (5)

Jared Smith
Jared Smith

Reputation: 21983

That's a thunk.

Essentially, it's a reified computation that you can pass around and evaluate on demand. There are all sorts of reasons one might want to delay evaluation of an expression (it may be expensive, it may have time-sensitive side effects, etc.).

Doing const enThunk = f => a => () => f(a); lets you pass around f(a) without actually evaluating it until a later point in time.

For a practical example, consider a fetch request. Now normally Promises start working as soon as they're constructed. But what if we want to retry the request if it fails? const response = fetch(someUrl); is done and on it's way but if we have const dataRequest = () => fetch(someUrl); the a retry is just calling the function again.

Upvotes: 10

Ousmane D.
Ousmane D.

Reputation: 56463

it's a higher-order function.

A higher-order function is a function that takes at least one or more functions as an input or returns another function.

This definition satisfies the code:

(f, a) => () => f(a)

as it's essentially a function returning another function.

Upvotes: -1

djfdev
djfdev

Reputation: 6037

In JavaScript, this is likely referred to as bind. There might be a more specific name for this type of combinator in general (which is very similar to the apply combinator -> f => a => f(a)).

Simple to implement:

const bind = (f, a) => () => f(a)

Upvotes: 0

Nina Scholz
Nina Scholz

Reputation: 386730

I would call it prepared function with deferred calling.

The first part takes the function and argument and returns a function without calling the given function with argument. This is called later with explicit calling of the function.

Upvotes: 1

corazza
corazza

Reputation: 32374

I'd call that a special case of binding

If you have a function of two parameters, say f(x, y), then you can define g(y) = f(5, y). In that case, you bound the parameter x in f to the fixed point 5.

Upvotes: 1

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