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FScript

Bindings and Immutability

Bindings use plain = and are immutable.

Basic bindings

answer = 42
name = 'Ada'

Rules:

  • bindings are block-scoped
  • rebinding the same name in the same scope is a compile error
  • shadowing in a nested inner scope is allowed
  • let, const, and var are not part of the language

Immutability is not just for names

Records and arrays are also immutable in Draft 0.1.

These are invalid:

user.name = 'Grace'
items[0] = 10

Instead, create new values:

import Object from 'std:object'


nextUser = Object.spread(user, { name: 'Grace' })

Why this matters

Immutability makes code easier to reason about and supports stronger compiler guarantees. It also fits naturally with FScript’s pipe-oriented and expression-oriented style.

Comparison to JavaScript or TypeScript

If you are used to mutable local variables, the main habit change is to model steps as new values:

trimmed = String.trim(text)
normalized = String.lowercase(trimmed)

That style is often clearer anyway because intermediate states are named explicitly.