- [WARNING] This programming language is still under active development and is not stable.
- Using it may cause unexpected behavior, memory leaks, or other critical issues.
- Many features are incomplete or experimental.
- It is strongly advised not to use this language in production or for important projects until development is fully completed and thoroughly validated.

🪐 Mercury Programming Language

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MercuryLang is a lightweight, free, and open-source programming language written in C++, inspired by the simplicity of Lua and Python. It provides clean syntax, dynamic typing, powerful standard libraries, and a fast interpreter — ideal for beginners and language creators alike.

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🚀 Features

• 🔹 Python-like clean syntax
• 🔹 First-class functions
• 🔹 Built-in math & list support
• 🔹 Dynamic variables and control flow
• 🔹 Interactive REPL + .mer file runner
• 🔹 C++ API to embed or customize MercuryLang

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🔨 Build from source

1. Navigate to the MercuryLang-main folder.

2. Open Command Prompt.

3. Run make to build from source, and mer, merc, mpi will be in MercuryLang-main/Bin/

4. Rename MercuryLang-main into MercuryLang and then move it to C:/

5. Edit environment path to C:/MercuryLang/Bin/

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⚙️ Getting Started

Prerequisites

• C++ Compiler (MSVC / GCC / Clang)
• CMake 3.12+

Running Mercury

mer           # Launch REPL
mer main.mer  # Run file

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🧠 Syntax Guide and Help

📤 Output

import "IO" # standard IO library

print("hello world") # output: hello world

🔢 Variables

import "IO"

let x = 10
print(x)

📋 String

import "IO"

let a = "hello, "
let b = "world"
print(a + b)

📋 Lists

import "IO"

let fruits = [["apple, "orange", "pineapple"], "banana", "water"]
fruit *= 2
print(fruits[0][1])

frutis[0][2] = "watermelon"

let other_food = ["fish", "egg"]
print(fruits + other_food)

🧠 Lambda

import "IO"

let f(x) = [1, 2, 3, 4, x]
print(f(3)[0])

🧠 Functions

import "IO"

func add(x, y) do
    return x + y
end

print(add(2, 3))

🔀 While loop

import "IO"

let x = 0
while x < 100 do
    print(x)
    x += 1
end

🔀 For loop

import "IO"

for i in range(0, 1000) do
    print(i)
end

🔀 Do loop

import "IO"

let x = 0
loop
    print(x)
    x += 1

    if x > 100 then
        break
    end
end

🔀 If-elif-else statement

import "IO"

let a = 1

if a == 1 then
    print("a = 1")
end

elif a == 2 then
    print("a = 2")
end

else
    print("other value")
end

📋 Classes

class Animal do
    let name = ""
    let age = 0

    func init_name(n, a) do
        this.name = n
        this.age = a
    end
end

class Dog extends Animal do
    name = "Dog"
    age = 12

    func bark() do
        print("woof")
    end
end

class Cat extends Animal do
    name = "Cat"
    age = 15
    
    func meow() do
        print("meow")
    end
end

let pup = Dog()
let kirby = Cat()

pup.init_name("Pup Dog", 16)
kirby.init_name("LongTail Cat", 20)

print(pup.name)
print(kirby.name)

🧠 Call C++ Functions from MercuryLang

MercuryLang supports calling C++ functions from dynamic libraries (.dll on Windows) via the dll_load function.

dll_load("<path_to_dll>", "<function_name>", [arg1, arg2, ...])

• <path_to_dll>: Path to your compiled DLL or shared library.
• <function_name>: Name of the exported C++ function.
• [arg1, arg2, ...]: Arguments passed to the C++ function (as a list).

---

🛠 Example: Extending Lists or Strings

1️⃣ C++ Implementation

#include <Mercury.h>  // Include Mercury API

START_DLL  // Required macro for Mercury DLL

// Exported function must return table* and accept table* args[]
DLL_EXPORT table* extend(table* args[]) {
    table *item1 = args[0];
    table *item2 = args[1];

    if (item1->is_list && item2->is_list) {
        item1->list_v->args.insert(item1->list_v->args.end(),
                                   item2->list_v->args.begin(),
                                   item2->list_v->args.end());
        item1->list_v->size += item2->list_v->size;
        return item1;
    }

    else if (item1->is_str && item2->is_str) {
        item1->f_str_v->buff.insert(item1->f_str_v->buff.end(),
                                    item2->f_str_v->buff.begin(),
                                    item2->f_str_v->buff.end());
        item1->f_str_v->size += item2->f_str_v->size;
        return item1;
    }

    else {
        item1->cval += item2->cval;
        item1->value += item2->value;
        return item1;
    }
}

END_DLL  // Required macro

2️⃣ MercuryLang Side

Compile the C++ file into a .dll (Windows), then call it from Mercury:

func extend(item1, item2) do
    return dll_load("init.dll", "extend", [item1, item2])
end

extend([1, 2, 3], [4, 5, 6])  # => [1, 2, 3, 4, 5, 6]
extend("Hello, ", "World!")   # => "Hello, World!"

---

📜 Other syntax

MercuryLang also supports many other syntax features such as break, return, continue, and, or, not, is, include, import, do, end, if, elif, else, while, for, loop, and more.

🎮 Game

• MercuryLang has a library for graphic and game (MGL)
• This code here is a example for a simple jumping game using MGL
• If you want to use the library graphic and game download SDL3.dll and then move it into ..\Bin

import "MGL" # import Mercury Game Library

screen_width = 500
screen_height = 500

screen_init(screen_width, screen_height)

cube_width = 50
cube_height = 50

cube_x = 0
cube_y = screen_height - cube_height

cube_vel = 5

cube_color = [255, 255, 255]

while true do
    screen_fill(0, 0, 0)

    screen_draw(cube_x, cube_y, cube_width, cube_height, cube_color[0], cube_color[1], cube_color[2])

    let key = get_key_char(key_pressed())

    if same(key, "a") then
        cube_x -= cube_vel
    end

    if same(key, "d") then
        cube_x += cube_vel
    end

    if cube_x >= screen_width - cube_width then
        cube_x = screen_width - cube_width
    end

    if cube_x <= 0 then
        cube_x = 0
    end

    screen_flip()
end

screen_quit()

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🧬 Embedding MercuryLang in C++

#include <Mercury.h>

int main() {
    let_S   = "gan";
    PRINT_S = "in";
    WHILE_S = "lap";
    IF_S    = "neu";
    THEN_S  = "thi";
    END_S   = "ketthuc";

    LANGUAGE = "MercuryLangTiengViet";
    AUTHOR   = "Dinh Son Hai";

    prompt();
}

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📕 library installation

If Python has pip, so MercuryLang has mpi

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🔍 What is mpi?

• mpi (Mercury Package Installer) is the official tool for installing external libraries in MercuryLang — just like pip in Python.

• Unlike Python or Lua which use centralized package markets,
  MercuryLang uses GitHub as the main source for libraries.

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🚀 How to install a library?

Installing a library with mpi is simple. Just type:

mpi --install https://github.com/author/repo

Example:

mpi --install https://github.com/dinhsonhai132/math

When done just import it:

import "math"

Replace author/repo with the actual GitHub repository of the library you want to install.

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📁 Required Files in a Library Repo

To be recognized as a valid MercuryLang library, the repository must contain:

1. main.mer

• This is the entry point of the library.
• If it’s missing or named incorrectly, mpi will reject the repo.

2. mpi.json

• A metadata file that describes the library.
• Example format:

{
  "name": "your-library-name",
  "version": "1.0.0",
  "description": "A short description of your library.",
  "author": "YourName"
}

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Made by dinhsonhai132