✈️ Flug ✈️

Now made with 100% more Kotlin!

Flug is a simple programming language made by Truttle1 to learn how programming language implementation works.

Features

Integer and Boolean Variables

You can declare variables like so:

let x = 3;
const y = true;

In this example, x is mutable, so later on you can write:

x = x + 1;

and change the value of x. y on the other hand is constant, so its value cannot be changed after it is created.

Flow Control Statements

Flug supports the following flow control statements:

if (<cond>) {
    doSomething()
}
elif (<another>) {
    somethingElse()
}
else {
    optional()
}

and

while (<cond>) {
    loop()
}

Semicolons

Flug is a language where everything is evaluated as an expression. Semicolons (;) exist to seperate Flug expressions, where the left side of the expression does side effects (like mutating variables) and the right side returns its expression to whatever comes next.

So:

if(x > y) {
    z = x
}
else {
    z = y
};
z

will set z to the result of the if statement and return z. Note that because the if-else statement is an expression on its own, it must end with a semicolon.

Functions

You can declare functions in flug like so:

const mutThenSum = func(const x, y) => {
    y = y * 2;
    x + y
};
mutThenSum(2, 3)

In this example, y is a mutable parameter, meaning it can be changed after it is assigned by the function (though it only changes the version in scope of the function. The original passed in is unaffected). x on the other hand cannot be changed in the function.

The function returns whatever expression the code within it evaluates to.

Flug does support recursion, and Flug functions are first class functions, so they are treated the same as other variable types.

Example

The following computes the sum of (3 + 2)! and the 7th Fibonacci number:

const factorial = func(const x) => {
    if(x <= 1) {
        1
    }
    else {
        x * factorial(x - 1)
    }
};

const fib = func(const x) => {
    if(x <= 1) {
        1
    }
    else {
        fib(x - 1) + fib(x - 2)
    }
};

fib(7) + factorial(3 + 2)