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Discussion on: Function vs Object

codemouse92 profile image
Jason C. McDonald • Edited on

From what I understood, the main complaint against stateful closures (would that be what you call them) is when you provide it with the same inputs, and get different outputs. Any function should provide the same output for the same input, every time.

But, as you pointed out, constants don't contribute that issue.

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stereobooster profile image
stereobooster Author • Edited on

Closure without mutation or re-assignment ("pure"):

const addSome = (x) => (y) => x + y;
const addFive = addSome(5);
addFive(1) === addFive(1) 

Closure with re-assignment += ("not pure"):

const counter = (x) => (y) => x += y;
const countFromZero = counter(0);
countFromZero(1) !== countFromZero(1)

My point is that there is nothing wrong with closures. It is re-assignment and mutation which make closures (or functions) "not pure".

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codemouse92 profile image
Jason C. McDonald

Yup, makes sense!

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bootcode profile image
Robin Palotai • Edited on

Re state: in pure FP I think we mean a "named" piece of data whose instances get changed over time:

go :: Int -> Int
go 0 = 0
go s = s + go (s-1)

Here s can be thought of as state, even though specific bindings of s don't change.

We observe state over the course of computation.