Quick start for JavaScript developers

Welcome to Wipple! This guide goes over some basic JavaScript concepts and their equivalent in Wipple. When you finish this guide, you’ll have a foundational understanding of Wipple code that you can use to experiment on your own.

Hello, world

Wipple’s equivalent of console.log is show:

show "Hello, world!"

Notice that there’s no semicolons in Wipple code — just put each statement on its own line.

Comments, numbers and strings

You can write a comment using --. Wipple only has line comments:

-- This is a comment
this is executed -- this is not

Numbers are represented in base 10 instead of floating point, but they are written the same way:


Strings are called “text” in Wipple, and must use double quotes:

"Hello, world!"
"line 1\nline 2"

You can use format to do string interpolation:

format "Hello, _!" "world" -- Hello, world!


In Wipple, you can declare variables using the : operator:

answer : 42
name : "Wipple"

Wipple uses static single assignment, which means that you can’t change the value of an existing variable after you create it. However, you can declare the same variable twice — the new variable shadows the old one:

x : 42
x : x + 1
show x -- 43

if statement

Wipple doesn’t have an if statement like in JavaScript. Instead, if works more like the ternary operator, and can be used anywhere an expression is needed. By convention, boolean variables end in a question mark.

password : "letmein123"
valid? : password = "password123!" -- use a single '=' to compare values
show (if valid? "Access granted" "Access denied") -- Access denied

Basic types

Wipple is a statically-typed language, which means that your code is verified at compile-time. Luckily, Wipple has type inference, so you usually don’t need to think about types at all! You can use :: to annotate the type of a value.

42 :: Number
"Hello" :: Text

If you mismatch the types, Wipple will emit an error:

42 :: Text -- mismatched types: expected `Text`, but found `Number`


Wipple calls objects “types”, which you can create using type:

Person : type {
    name :: Text
    age :: Number

You can create an instance of this object like so:

bob : Person {
    name : "Bob"
    age : 35

And you can use destructuring to get the inner values:

{ name age } : bob


Wipple’s functions work like JavaScript’s arrow functions. In fact, they both use the arrow notation!

increment : x -> x + 1
show (increment 42) -- 43

One big difference is that Wipple functions may only accept a single parameter. If you want multiple parameters, use multiple functions!

add : a -> b -> a + b
show (add 1 2) -- 3

If that’s confusing, here’s the equivalent JavaScript code:

const add = (a) => (b) => a + b;
console.log(add(1)(2)); // 3


Wipple doesn’t allow you to add methods to an object (although you can store functions inside types like any other value). Instead, you can declare functions like this:

greet :: Person -> Text
greet : { name } -> format "Hello, _!" name

greet bob -- Hello, Bob!

Alternatively, you can use the . operator to chain function calls:

bob . greet -- Hello, Bob!


Wipple has neither classes nor inheritance. Instead, you can use traits! Traits are pretty advanced, but here’s a simple example in TypeScript and in Wipple:


// Greet is an interface that can be implemented with a function returning text
interface Greet {
    greet(): string;

// For any value implementing Greet, return a greeting
function greet<A extends Greet>(x: A): string {
    return `Hello, ${x.greet()}`;

class Person implements Greet {
    name: string;

    constructor(name: string) {
        this.name = name;

    // Greet for Person values is defined as the person's name
    greet() {
        return this.name;

class Earth implements Greet {
    constructor() {}

    // Greet for Earth values is defined as "world"
    greet() {
        return "world";

greet(new Person("Bob")); // Hello, Bob!
greet(new Earth()); // Hello, world!


-- Greet is a trait that can be defined with a function returning text
Greet : A => trait (A -> Text)

-- For any value where Greet is defined, return a greeting
greet :: A where (Greet A) => A -> Text
greet : x -> format "Hello, _!" (Greet x)

Person : type {
    name :: Text

-- Greet for Person values is defined as the person's name
instance (Greet Person) : { name } -> name

Earth : type

-- Greet for Earth values is defined as "world"
instance (Greet Earth) : just "world"

show (greet (Person { name : "Bob" })) -- Hello, Bob!
show (greet Earth) -- Hello, world!