Add sugar for dereferencing

[amiralies]

happened to write a heavily mutable code and using .contents everywhere was a pain. a sugar like ml's ^ makes reading and writing mutable code with refs much easier

[mununki]

Not sure I understand correctly. If you mean ! in OCaml for dereferencing of ref, I think the operators for deref and mutate functions are needed in the syntax layer.

let foo = ref("")
let deref = r => r.contents // `!` in OCaml
let mutate = (r, value) => r.contents = value // `:=` in OCaml
let bar = ^foo // deref(foo)
let baz = foo := "baz" // mutate(foo, "baz")
// `^` and `:=` are just examples.

[amiralies]

yes. := is available today

[stale[bot]]

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