Not all features mentioned here are implemented

The basic language syntax of Loop will be explained here. Only the very basics will be explained here. If the feature has more to it a link to the documentation entry will be provided for more detail.

Entry Point

Every Loop program will start with the file provided when invoking the Loop executable.

For example, this in example.loop and invoking it with ./loop example.loop will print "Hello World!"

println("Hello World!")

Standard Input & Output

To read from standard input (stdin) and write to standard output (stdout) Loop provides some easy helpers.


For input you can use the input function. For example to accept user input without a prompt:

// Variable "test" will contain the value of what the user typed in.
test := input("")

You can also accept user input with a prompt, for example:

// Variable "test" will contain the value of what the user typed in.
test := input("Prompt > ")


It's extremely simple to output to stdout. There are two built-in functions for this.


Allows you to directly print to stdout without a newline.

// No new line, results in "Hello World!"
print(" World!")

// Explicit new line
print("Hello World!\n")


Allows you to print to stdout with an implicit new line.

// Implicit new line
println("Hello World!")

// Implicit & Explicit new line (results in two new lines)
println("Hello World!\n")


In Loop every expression can be assigned to a variable for future reference. This includes things like functions and loops. Declaring a variable is simple and concise.

The most basic feature is assigning an integer to a variable.

x := 100;

It's also possible to assign functions and then call it. Calling a function requires parenthesis. Without them, it will result in the function reference being returned.

// Defines a new function named "func"
func := fn() {}

// Calls the function "func", notice the parenthesis

More about Variables


A function is a a simple way to bundle common instructions that might need an alternate input. Defining a function is a simple, for example to create a function that doubles it's input:

// Defines a new function called double with one parameter named "x"
fn double(int x) {
  // Returns the input "x" multiplied by 2
  return x * 2

// Evaluates to 200

More about Functions

Implicit Returns

Most other languages require you to specify the return keyword to return an expression from a function, however in Loop this is not neccesary. Allowing syntax like the following.

// This works the same as the previous chapters example
fn double(int x) {
  x * 2

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