Forge (フォージ)

A simple compiler written in Python.

Table of Contents

1. About
2. Pipeline Overview
3. Features
4. Notes
5. Roadmap
6. Examples
7. References

About

Forge is an educational personal project designed to help understand how programming languages work under the hood.

Pipeline Overview

1. Lexical Analysis - Converts source text into a stream of tokens.
2. Parser - Reads tokens and builds an Abstract Syntax Tree (AST).
3. Semantic Analysis - Checks types, scopes, and ensures valid constructs.
4. Intermediate Representation - Transforms the AST into a lower-level representation for optimisation.
5. Register Allocation - Assigns values to virtual registers effectively.
6. Virtual Machine - Executes the compiled code in a custom runtime environment.

Features

• Responsive error messages
• Custom builtin functions
• Optimisations: Dead Code Elimination (DCE), Constant Folding (CF)

Notes

• This is just self-driven personal project, meaning:
  • The code will be messy
  • There will be bugs
  • It is not supposed to be easy to use
• In the latest commit, main.py is hardcoded to output many debug statements, thus this repo is not meant for beginners.

初心者向けではありません。デバッグ用出力が多く、コードも整理されていません。

Roadmap

Planned improvements:

Feature	Priority	Notes
Additional optimisation passes	low
Hashmaps	high	map["key"] = value
Real types instead of Python types	medium	Support for custom types
Compile to bytecode	low
String interpolations	medium	Supports defining variables inside strings

Examples

Below are some example code snippets that Forge can compile / run.

Functions, variables, and builtin functions

fn check(a, b) {
if a == b {
return "A is equal to B"
} else {
return "A is not equal to B"
}
}
result = check(2, 5)
println(result)

Expected output:

A is not equal to B

While loops, continues + breaks, and builtin functions

i = 0
while i < 10 {
i = i + 1
if i == 3 { continue }
if i == 7 { break }
println(i)
}

Expected output:

1
2
4
5
6

References

• Creating Your Own Programming Language with Dr Laurie Tratt - Computerphile
• Crafting Interpreters - Robert Nystrom