Types

Husk uses static types for source checking and erases most type information in the generated JavaScript.

Primitive Types

Core primitive types are:

• i32
• i64
• f64
• bool
• String
• ()

Integer and float types are checked by Husk. JavaScript output uses native numbers where possible and runtime helpers where the compiler needs special handling.

Structs and Enums

Structs are nominal record types:

struct User {
    id: String,
    name: String,
}

Enums support unit and payload variants:

enum Result<T, E> {
    Ok(T),
    Err(E),
}

Enums compile to tagged JavaScript objects and can be checked exhaustively in match expressions.

Generics

Generic types and functions are type-checked but erased at runtime:

fn first<T>(items: [T]) -> Option<T> {
    if items.len() > 0 {
        Some(items[0])
    } else {
        None
    }
}

All instantiations share the same JavaScript implementation.

JavaScript Types

The standard JavaScript interop types are opaque wrappers:

• JsValue
• JsArray<T>
• JsPromise<T>
• JsFn
• JsObject

Use these for imported JS values that do not map cleanly to Husk. Prefer wrapping them behind named Husk functions or structs before using them in app logic.

TypeScript Imports

The d.ts importer maps TypeScript declarations into the closest Husk shape it can represent. Simple functions, interfaces, classes, arrays, promises, and literal unions can often become typed declarations. Complex unions, intersections, conditional types, any, and unknown may become JsValue.

This is intentional: imported JavaScript values remain shared and mutable, and Husk does not try to emulate the full TypeScript type system.