Let Binds

Let bindings introduce names that are visible in their scope after they are defined.

let x = 2 + 2 + x; // compile error x isn't defined yet
let y = x + 1 // ok

The same name can be used again in the same scope, it will shadow the previous value.

let x = 1;
let x = x + 1; // ok uses the previous definition
x == 2 // true

You can annotate the binding with a type, which will then be enforced at compile time. Sometimes this is necessary in order to help type inference.

let x: Number = 1; // note x will be of type Number even though it's an i64
let y: string = x + 1; // compile time type error

You can use patterns in let binds as long as they will always match.

let (x, y) = (3, "hello"); // binds x to 3 and y to "hello"
x == 3; // true
y == "hello" // true

You can mix type annotations with pattern matches

let (x, y): (i64, string) = (3, "hello")

You can assign documentation to a let bind using a /// comment. Documentation will be displayed in the shell when the user tab completes and will be made available by the lsp server.

// this is a normal comment
let x = 1;
/// this is documentation for y
let y = 2;