Classes Types

Utility Class#

We first introduce the simplest utility class. Utility classes serve as collections of functions. For example, we should put some math functions inside a Math utility module. i.e.

class Math {
function plus(a: int, b: int): int = a + b
function cosine(angleInDegree: int): int = panic("Not supported!")

Here you see how you would define functions. Each top-level function defined in the module should have type-annotations for both arguments and return type for documentation purposes. The return value is written after the = sign. Note that we don't have the return keyword because everything is an expression.

A utility class is implicit a class with no fields.

There is a special kind of function called method. You can define methods in utility classes although they are not very useful.

Primitive and Compound Types#

You already see two several primitive types: string and int. There are 4 kinds of primitive types: unit, int, string, bool.

The unit type has only one possible value, which is {}. It's usually an indication of some side effects. The int type includes all 64-bit integers. The string type includes all the strings quoted by double-quotes, like "Hello World!". The bool types has two possible values: true and false.

samlang enables you to use these primitive types to construct more complex types. You can also have tuple types like [int, bool, string] and function types like ((int) -> int, int) -> int.

You may want to have some named tuple so that the code is more readable. samlang allows that by letting you create an object class.

Object Class Module#

Here we introduce the first kind of class module: object class module. You can define it like this:

class Student(private val name: string, val age: int) {
method getName(): string =
private method getAge(): int = this.age
function dummyStudent(): Student = { name: "RANDOM_BABY", age: 0 }

The module shown above defines a function, 2 methods, and a type Student. You can see that the type Student is already used in the type annotation of dummyStudent function. You can create a student object by the JavaScript object syntax as shown above. This kind of expression can only be used inside the module.

You can also see methods defined here. You can think of method as a special kind of function that has an implicit this passes as the first parameter. (You cannot name this as a parameter name because it's a keyword.)

The private keyword tells the type-checker that this function, field or method cannot be used outside of the class that defines it.

Variant Class Module#

Object class module defines a producct type; variant class module defines a sum type. With variant class module, you can define a type that can be either A or B or C. Here is an example:

class PrimitiveType(
) {
// some random functions
function getUnit(): PrimitiveType = U({})
function getInteger(): PrimitiveType = I(42)
function getString(): PrimitiveType = S("Answer to life, universe, and everything.")
function getBool(): PrimitiveType = B(false)
// pattern matching!
method isTruthy(): bool =
match this {
| U _ -> false
| I i -> i != 0
| S s -> s != ""
| B b -> b

Inside the module, you can construct a variant by VariantName(expr).

Each variant carries some data with a specific type. To perform a case-analysis on different possibilities, you can use the match expression to pattern match on the expression.


Generics is supported in all kinds of modules. Here are some examples.

class FunctionExample {
function <T> getIdentityFunction(): (T) -> T = (x) -> x
class Box<T>(val content: T) {
function <T> init(content: T): Box<T> = { content } // object short hand syntax
method getContent(): T = {
val { content } = this; content
class Option<T>(None(unit), Some(T)) {
function <T> getNone(): Option<T> = None(unit)
function <T> getSome(d: T): Option<T> = Some(d)
method <R> map(f: (T) -> R): Option<R> =
match (this) {
| None _ -> None(unit)
| Some d -> Some(f(d))