Quick overview: Let Bindings
A "let binding" binds values to names. In other languages they might be called a "variable declaration". The binding is immutable and can be referenced by code that comes after them.
let greeting = "hello!";
let score = 10;
let newScore = 10 + score;
Note: If you are coming from JavaScript, these bindings behave like const,
not like var orlet.
Bindings are Immutable
Reason let bindings are "immutable", they cannot change after they are created.
let x = 10;
/* Error: Invalid code! */
x = x + 13;
Binding Shadowing
Bindings can be shadowed to give the appearance of updating them. This is a common pattern that should be used when it seems like a variable needs to be updated.
let x = 10;
let x = x + 10;
let x = x + 3;
/* x is 23 */
Block Scope
Bindings can be manually scoped using {}.
let message = {
let part1 = "hello";
let part2 = "world";
part1 ++ " " ++ part2
};
/* `part1` and `part2` not accessible here! */
The last line of a block is implicitly returned.
Mutable Bindings
If you really need a mutable binding then check out the ref feature.