Compilers and Interpreters

Build a fully RFC 8259-compliant JSON parser from scratch. You'll tokenize structural characters, decode escape sequences and Unicode, parse numbers with strict grammar, and recursively assemble objects and arrays. By the end you'll deeply understand how json.loads, JSON.parse, and every other parser actually works.

Build a Markdown parser following CommonMark: headings, paragraphs, emphasis, links, images, lists, code blocks, blockquotes, horizontal rules. Then add GFM extensions (tables, strikethrough). The foundation of every README, blog post, and static site generator.

Build a regex engine from first principles — literal matching, character classes, quantifiers, anchors, alternation, capture groups. You'll implement Thompson's NFA construction (1968!) and the parallel simulation algorithm that guarantees linear time. By the end you'll understand what makes RE2, Go's regexp, and Rust's regex crate fast and safe.

Build a Jinja2-style template engine: tokenize {{ var }} and {% tag %}, parse to AST, resolve variables, apply filters with auto-escaping, evaluate if/for control flow, and implement template inheritance with extends/block. Powers Flask, Ansible, Salt, Helm.

Build a Wadler-style pretty printer like prettier/black/gofmt: parse to AST/CST, define a Doc algebra (text/line/group/nest), make line-break decisions based on width, preserve comments through formatting, support hanging indent + alignment. The toolchain backbone of every modern codebase.

Build an ESLint/Pylint-style static analyzer: tokenize source, build an AST, walk it with visitor pattern, check naming/complexity/unused names/dead code, parse suppressions, load config from pyproject.toml, emit human/JSON/GitHub formats. The toolchain backbone of every modern codebase.

Build a Scheme/Lisp interpreter in ~200 lines: tokenize, parse to nested lists, evaluate atoms and expressions, support define and if, lambda + closures, recursion, list operations, and macros. The textbook (SICP) classic — every CS curriculum has this.

Build a C compiler from scratch: lexer, recursive-descent parser, type checker, IR generation, x86-64 code generation, optimization passes (constant folding, dead code, register allocation), and linking. Builds the full pipeline like chibicc, GCC, and Clang.