compiler-old/PLAN.md

Compiler Roadmap

A Rust-flavored, C-targeting language - built pipeline-first.

Implementation language: Rust
Code generation target: x86-64 (AT&T / Intel syntax .s → assembled via GAS or NASM)

Phase 1 - Lexer

• Define token enum (int literal, bool literal, ident, keywords, operators, punctuation)
• Implement character-by-character scanner loop
• Handle whitespace & single-line comments (//)
• Produce source spans (file, line, col) on every token
• Unit-test: known inputs → expected token streams

Phase 2 - Parser

• Write grammar for the base subset
  • fn declarations, return, int/bool literals
  • Arithmetic (+, -, *, /)
• Implement recursive-descent parser
• Attach source spans to every AST node
• Emit structured parse errors with span info
• Unit-test: parse valid snippets, expect correct AST shapes

Phase 3 - Semantic Analysis

• Implement scope-aware symbol table
• Name resolution pass - resolve all Ident nodes to their declarations
• Type inference / checking for int and bool
• Validate function return types match declared signature
• Error on use-before-declaration and undeclared symbols
• Unit-test: ill-typed programs produce correct diagnostics

Phase 4 - x86-64 Code Generation

• Design a simple intermediate representation (linear IR, or use AST directly)
• Implement stack-frame layout for local variables
• Emit System V AMD64 ABI-compliant function prologues / epilogues
• Codegen for arithmetic & comparison expressions
• Codegen for function calls (argument passing via registers)
• Codegen for return statements
• Output .s file, assemble with NASM / GAS
• End-to-end test: compile a simple fn → run → correct exit code

Planned Features (Backlog)

Control flow

• if / else branching
• while loops

Types & memory

• Typed pointers (*T)
• Opaque pointers (*void / *opaque)
• Raw pointer arithmetic & dereference
• Fixed-size arrays ([T; N])
• Slices (&[T] / []T)

Composite types

• Structs & field access
• Enums (C-style tagged unions)
• Pattern matching (match / switch)

Strings & interop

• String literals & *u8 handling
• Variadic functions (for printf interop)
• extern / FFI declarations

Tooling & backend

• Proper register allocator
• Debug info (DWARF)
• Standard library bootstrap (print, malloc wrapper)