How to Build a Compiler or Interpreter from Scratch: A Complete Guide

Building a compiler or interpreter from scratch requires implementing a multi-stage pipeline that transforms source code into tokens, constructs an abstract syntax tree, performs semantic analysis, and either generates target code or executes the tree directly.

Creating your own programming language implementation is one of the most rewarding challenges in computer science. The sdmg15/Best-websites-a-programmer-should-visit repository curates a comprehensive collection of resources specifically for developers who want to build a compiler or interpreter from scratch, covering everything from theoretical foundations to working code examples.

Understanding the Fundamentals of Compiler Construction

Before writing code, you need to understand the theoretical underpinnings of language implementation. The repository references classic texts like the Dragon Book (Compilers: Principles, Techniques, and Tools) alongside modern tutorials that explain lexical analysis, parsing algorithms, abstract syntax trees (ASTs), and code generation strategies.

The Core Pipeline: From Source Code to Execution

Every compiler or interpreter follows a structured pipeline. The resources in the README.md file under the "Building a Simple Compiler/Interpreter" section break this down into six essential stages.

Lexical Analysis (Tokenization)

The first stage converts raw source text into a stream of tokens. This involves writing a lexer that recognizes keywords, identifiers, operators, and literals using regular expressions or finite automata.

Parsing and Abstract Syntax Trees

Next, a parser consumes the token stream to build an abstract syntax tree (AST). This stage validates grammatical structure according to your language's formal grammar, typically defined in EBNF or using parser generators like ANTLR or Bison.

Semantic Analysis

After parsing, the compiler performs semantic analysis to check type consistency, resolve variable scopes, and enforce language-specific validations before execution or code generation.

Code Generation or Direct Interpretation

Finally, you either generate target code (transpiling to C, emitting LLVM IR, or producing machine code) or interpret the AST directly by walking the tree and evaluating nodes at runtime.

Practical Resources in the Repository

The sdmg15/Best-websites-a-programmer-should-visit repository aggregates high-quality learning materials in its README.md file. These include:

• Video tutorials: YouTube playlists that demonstrate building a tiny expression interpreter in Python, walking through lexer and parser implementation.
• Written guides: Step-by-step articles that construct a minimal compiler for a C-like language, covering the full pipeline from tokens to assembly.
• Open-source projects: Links to GitHub repositories containing simple Lisp interpreters and tiny C-like compilers that you can clone, run, and extend.

Hands-On Example: A Minimal Arithmetic Interpreter

To illustrate the concepts, here is a complete Python implementation of a recursive-descent interpreter for arithmetic expressions. This example demonstrates the lexing and parsing stages described in the repository's resources:

import re

# Token specification

TOKEN_SPEC = [
    ("NUMBER",   r"\d+(\.\d*)?"),   # Integer or decimal number

    ("PLUS",     r"\+"),            # Addition

    ("MINUS",    r"-"),             # Subtraction

    ("TIMES",    r"\*"),            # Multiplication

    ("DIVIDE",   r"/"),             # Division

    ("LPAREN",   r"\("),            # Left parenthesis

    ("RPAREN",   r"\)"),            # Right parenthesis

    ("SKIP",     r"[ \t]+"),        # Skip whitespace

]

TOK_REGEX = "|".join("(?P<%s>%s)" % pair for pair in TOKEN_SPEC)
Token = re.Match

def lexer(text):
    for mo in re.finditer(TOK_REGEX, text):
        kind = mo.lastgroup
        if kind == "NUMBER":
            yield ("NUMBER", float(mo.group()))
        elif kind != "SKIP":
            yield (kind, mo.group())

# Recursive‑descent parser / evaluator

class Parser:
    def __init__(self, tokens):
        self.tokens = iter(tokens)
        self.current = None
        self.advance()

    def advance(self):
        self.current = next(self.tokens, ("EOF", None))

    def expr(self):
        value = self.term()
        while self.current[0] in ("PLUS", "MINUS"):
            op = self.current[0]
            self.advance()
            rhs = self.term()
            value = value + rhs if op == "PLUS" else value - rhs
        return value

    def term(self):
        value = self.factor()
        while self.current[0] in ("TIMES", "DIVIDE"):
            op = self.current[0]
            self.advance()
            rhs = self.factor()
            value = value * rhs if op == "TIMES" else value / rhs
        return value

    def factor(self):
        if self.current[0] == "NUMBER":
            val = self.current[1]
            self.advance()
            return val
        elif self.current[0] == "LPAREN":
            self.advance()
            val = self.expr()
            if self.current[0] != "RPAREN":
                raise SyntaxError("Missing ')'")
            self.advance()
            return val
        else:
            raise SyntaxError(f"Unexpected token: {self.current}")

def evaluate(expr):
    tokens = lexer(expr)
    parser = Parser(tokens)
    return parser.expr()

# Example usage

print(evaluate("3 + 4 * (2 - 1)"))   # → 7.0

This implementation follows the classic pipeline found in the repository's curated materials: lexing with regular expressions, parsing via recursive descent, and evaluation by traversing the implicit AST formed by the call stack.

Navigating the Repository Structure

When exploring the sdmg15/Best-websites-a-programmer-should-visit repository, focus on these key files:

• README.md: Contains the "Building a Simple Compiler/Interpreter" section with all curated links to tutorials and projects.
• package.json: Project metadata for CI tooling.
• _config.yml: Jekyll configuration for the GitHub Pages site.
• white_listed_sites.txt: URLs approved for the site's embed feature.

Summary

Building a compiler or interpreter from scratch requires implementing a structured pipeline that transforms source code into executable behavior. Key takeaways from the curated resources include:

• Master the fundamentals of lexical analysis, parsing theory, and AST construction before writing code.
• Follow the six-stage pipeline: lexing, parsing, semantic analysis, and either code generation or direct interpretation.
• Leverage parser generators like ANTLR or Bison for complex grammars, or write recursive-descent parsers for simpler languages.
• Study the open-source examples linked in the repository's README.md to see working implementations of Lisp interpreters and C-like compilers.
• Start with an arithmetic interpreter (like the Python example above) to validate your understanding before tackling full language features.

Frequently Asked Questions

What programming language should I use to build a compiler?

You can build a compiler or interpreter in any Turing-complete language, but Python, C++, and Rust are popular choices. Python offers rapid prototyping for educational interpreters, while C++ and Rust provide memory safety and performance for production compilers. The repository links to examples in multiple languages, including JavaScript and Go.

Do I need to know assembly language to build a compiler?

Knowing assembly language is only necessary if you are targeting machine code directly or writing a backend for a specific architecture. Many educational compilers target higher-level languages like C or LLVM IR, which abstracts away assembly details. However, understanding assembly helps optimize code generation and is valuable for systems programming roles.

How long does it take to build a simple compiler from scratch?

A basic arithmetic interpreter can be built in a few hours, while a simple compiler for a C-like language typically takes 2–4 weeks of focused effort. A production-quality compiler with optimizations, multiple backends, and standard libraries can take years of development. The repository's curated tutorials are designed to help you build a working prototype within a weekend.

What is the difference between a compiler and an interpreter?

A compiler translates source code into target code (machine code, bytecode, or another high-level language) ahead of time, creating a standalone executable. An interpreter directly executes the source code or AST without prior translation, processing statements one at a time. Some languages use both: Java compiles to bytecode which is then interpreted or JIT-compiled by the JVM.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}