[runeks]

> I think the concept of immutability confuses people.

I think it confuses people because it’s framed oddly. Immutability isn’t about being unable to mutate state, it’s about no longer using containers (registers) as variables, such that the equal operator actually means “equals” as opposed to “store”.

In most programming languages, the equal operator works as a “store” operation, which stores a value in a named container/register. In “immutable by default” languages like Haskell, the equal operator actually means “equals”, as in “is synonymous with”.

The essence of immutability is referencing values directly, through synonyms, as opposed to storing them in named registers for later retrieval. When it’s done this way, immutability no longer makes sense: is the number 3 mutable? Can the number 3 be mutated into 4, or are they just two distinct numbers?

[canes123456]

I think I understand the point you are making but this is way more confusing for me. Partly this can be blamed on imperative lanuages and = vs ==.

[sbergot]

Not that in mutable languages == can either mean storage equality or value equality. In immutable languages there is only value equality.

[giesch]

In a procedural language:

x == 3 means: Take the value out of the box x. Is it 3?

x = 3 means: x is a box, put 3 in it. The 3 lasts forever, or until someone changes it.

In a functional language:

x = 3 means: Take the value out of box x. Is it 3?

let x = 3 in [...] means: x is a box, put a 3 in it. The 3 lasts for only the [...], but cannot be undone.

[nybble41]

Correction: In a functional language (specifically Haskell):

  x = 3 means: x is defined as 3.
  x == 3 means: Is x equal to 3?
  let x = 3 in [...] means: within the scope of [...], x is defined as 3.

There is no specific point where something is "put into the box" or "taken out of the box". In fact, there is no "box". The functional programming concept of "bindings" does not correspond to the imperative concept of "variables", not even the oxymoron known was "constant variables". (If you want variables in Haskell you need IORef or STRef, where the load and store operations are explicit monadic actions.)