Ref: Work with mutable state

The core data structures in Pointless are immutable. References serve as mutable wrappers around these values, allowing programs to leverage mutability. Note that references must not reference themselves (they must not contain circular references) as this could cause memory leaks and infinite recursion.

An example pseudorandom number generator function that uses a reference to store the generator state.

seed = Ref.of(0)

-- Linear congruential generator parameters
m = 2 ** 32
a = 1664525
c = 1013904223

fn random()
  next = (a * Ref.get(seed) + c) % m -- Calculate new seed
  Ref.set(seed, next) -- Store new seed
  next / m -- Return scaled value
end

random()
random()
random()
random()

panic: variable is not defined
name: Ref

seed = Ref.of(0)
       ^
At pages/stdlib/Ref/index.md:embedded:1:8

Module Contents

`Ref.get(ref)`

Get the value stored in ref.

Ref = import "std:Ref"
score = Ref.of(0)
Ref.get(score)

`Ref.of(value)`

Create a mutable reference containing value.

Ref = import "std:Ref"
Ref.of(0)

Ref.of(0)

`Ref.put(value, ref)`

Update ref to store value. Return value.

Ref = import "std:Ref"
score = Ref.of(0)
Ref.put(1, score)
score

1
Ref.of(1)

`Ref.set(ref, value)`

Update ref to store value. Return ref.

Ref = import "std:Ref"
score = Ref.of(0)
Ref.set(score, 1)
score

Ref.of(1)
Ref.of(1)

Set