The Lemon Programming Language

Lemon is a tiny, fast, interpreted language. This repository contains the source code for the Lemon interpreter, written in Go. The language is still in development, and the interpreter is not yet feature-complete. A peek at the REPL atm:

Hello, Lemon!

let message = "Hello, Lemon!";
print(message);

For more examples, check out the examples directory.

let fibonacci = fn(x) {
  if (x == 0) {
    0
  } else {
    if (x == 1) {
      return 1;
    } else {
      fibonacci(x - 1) + fibonacci(x - 2);
    }
  }
};
let map = fn(arr, f) {
  let iter = fn(arr, accumulated) {
    if (len(arr) == 0) {
      accumulated
    } else {
      iter(rest(arr), push(accumulated, f(first(arr))));
    }
  };
  iter(arr, []);
};
let numbers = [ 1, 1 + 1, 4 - 1, 2 * 2, 2 + 3, 12 / 2 ];
map(numbers, fibonacci);
// => returns: [1, 1, 2, 3, 5, 8]

Features

• Data types: boolean, integer and string
• Variables let name = value;
• Arithmetic operations (+, -, *, /)
• Logical operations (!, &&, ||)
• Functions fn (args) { body }
• First-class functions (closures)
• Comparison operations (==, !=, >, >=, <, <=)
• Control structures
  • if, else if (condition) { body } else { body }
  • else if branch
  • switch, case
  • match, when
  • while, for, loop
  • break, continue
• Garbage collection
• Strings let name = "value";
• String concatenation "value" + "value";
• Arrays [1, 2, 3]
• Hash maps { "key": "value" }
• Comments
• Error handling
• Standard library
• Modules
• Classes
• Generics
• Multithreading

Usage

To run the REPL, use the following command:

go run main.go

To build the interpreter, use the following command:

go build

Running lemon files (after building):

lemon example.mm

To run tests, use the following command:

go test <directory>