1 unstable release

new 0.1.0	Mar 22, 2025

#478 in Command line utilities

MIT license

510KB
10K SLoC

Welcome to Mechylang!

Mechylang was created because I wanted to learn how human written code gets turned into machine understandable code. This is a very simple language and is not meant to be used for anything other than learning.

This is a work in progress and is not ready for use yet.

Thanks to Writing an Interpreter in Go for helping me learn how to write an interpreter.

Features

Basic arithmetic
Variables
Functions
Functions as first class citizens
Closures
If statements
For loops
While loops
Arrays
Objects
Strings
Modules
Standard library

How to use Mechylang

First you'll need to install the interpreter.

cargo install --locked --git https://github.com/Dutch-Raptor/mechylang

Then you can run a file with the interpreter.

mechylang_cli file <file>

If you want to run a repl, you can do that too.

mechylang_cli repl

Syntax

Getting Started

Of course, every language needs a hello world program.

// This is a comment
// With the print function you can print to stdout
print("Hello World!");

Variables

To create a variable, you use the let keyword.

let x = 5;
let y = 10;
let z = x + y;

Valid variable names are any combination of letters, numbers, and underscores, but they must start with a letter or underscore.

let _x = 5;
let x1 = 10;
let x_1 = 15;
let x = 20;

Variables are mutable, so you can change their value.

Variable mutability being the default may change in the future.

let x = 5;
x = 10;

Functions

Functions are created with the fn keyword.

let add = fn(x, y) {
  return x + y;
};

let result = add(5, 10); // result = 15

Functions are first class citizens, so you can pass them around like any other value.

let apply = fn(f, x, y) {
  return f(x, y);
};

let add = fn(x, y) {
  return x + y;
};

let result = apply(add, 5, 10); // result = 15

This goes for builtin functions too.

let apply = fn(f, x) {
  return f(x);
};

let result = apply(len, "Hello World!"); // result = 12

Functions can also be returned from other functions.

let adder = fn(x) {
  return fn(y) {
    return x + y;
  };
};

let add5 = adder(5);
let result = add5(10); // result = 15

If Statements

If statements are pretty standard.

let x = 5;

if (x == 5) {
  print("x is 5");
} else {
  print("x is not 5");
}

The else statement is optional.

let x = 5;

if (x == 5) {
  print("x is 5");
}

Support for else if statements may be added in the future.

Loops

In Mechylang, there are two types of loops: for loops and while loops. These loops are expressions, so they return can return a value.

For Loops

To create a for loop, use the syntax for <variable> in <iterable> { <body> }.

for i in [1, 2, 3] {
  print(i);
}

// or use a range
for i in 0..3 {
  print(i);
}

More information on ranges can be found in the Ranges section. More information on iterables can be found in the Iterables section.

While Loops

To create a while loop, use the syntax while <condition> { <body> }.

let x = 0;

while (x < 10) {
  print(x);
  x = x + 1;
}

Break and Continue

You can use the break and continue keywords to break out of a loop or skip to the next iteration.

for i in 0..10 {
  if (i == 5) {
    break;
  }
  print(i);
}

for i in 0..10 {
  if (i % 2 == 0) {
    continue;
  }
  print(i);
}

You can also break with a value. This value will be returned from the loop. This is where it becomes important that loops are expressions.

let x = for i in 0..10 {
  if (i == 5) {
    break i;
  }
  print(i); // prints 0, 1, 2, 3, 4
};

print(x); // x = 5, prints 5

Arrays

Arrays are created with the syntax [<value>, <value>, ...].

let x = [1, 2, 3];

Arrays are 0 indexed, so you can access the first element with x[0].

let x = [1, 2, 3];
let y = x[0]; // y = 1

Arrays are not mutable yet, but this may change in the future.

Strings

Strings are created with the syntax "<value>".

let x = "Hello World!";

Iterables

Iterables are anything that can be iterated over. This includes arrays and ranges.

Ranges

Ranges are created with the syntax [start]..[[=]end]. Here anything in brackets is optional.

let x = 0..3; // 0 <= x < 3
let y = 0..=3; // 0 <= y <= 3
let z = ..3; // z < 3
let a = (6..); // a >= 6
let b = (..); // b is all integers
let c = ..=9; // c <= 9

Note that ranges that are open ended on the right require parentheses. Note that ranges that are open ended on the left are not iterable as there is no starting point.

Iterating

To iterate over an iterable, you can use a for loop.

for i in 0..10 {
  print(i);
}

Comments

// This is a comment
/* This is a multiline comment */

Examples

FizzBuzz

let fizzbuzz = fn(n) {
  for i in 1..=n {
    if (i % 3 == 0 && i % 5 == 0) {
      print("FizzBuzz");
      continue;
    }

    if (i % 3 == 0) {
      print("Fizz");
      continue;
    }

    if (i % 5 == 0) {
      print("Buzz");
      continue;
    }

    print(i);

  }
};

fizzbuzz(100);

Fibonacci

Recursive

let fib = fn(n) {
  if (n == 0) {
    return 0;
  }

  if (n == 1) {
    return 1;
  }

  return fib(n - 1) + fib(n - 2);
};

fib(10); // 55

Dynamically Programmed

let fib = fn(n) {
  let a = 0;
  let b = 1;

  for i in 0..n {
    b = a + b;
    a = b - a;
  }

  return a;
};

fib(10); // 55

Dependencies

~7–15MB
~192K SLoC