🐍 Viper

A fast Python interpreter written from scratch in Rust. Hand-rolled lexer, recursive-descent parser, bytecode compiler with peephole optimization, and a register-style VM that beats CPython 3.12 on 9 out of 10 benchmarks.

Quick Start

# Run a Python file
cargo run --release -- script.py

# Interactive REPL
cargo run --release

# Run benchmarks
cargo run --release --bin benchmark

Features

• Full pipeline: Lexer → Parser → AST → Bytecode Compiler → VM
• Bytecode VM with flattened frame layout, unified locals stack, raw-pointer code references
• Peephole optimizer fusing 4-instruction and 2-instruction hot-path sequences into superinstructions
• Interactive REPL with multi-line block support
• Supported Python subset: integers, floats, strings, booleans, lists, dicts, None, functions, if/elif/else, while, for..in, break/continue, def/return, print, augmented assignment, comparison chains, and/or/not

Performance vs CPython 3.12

Benchmarked on Apple Silicon (M-series), --release mode:

Benchmark	Viper	CPython 3.12	Speedup
5k arithmetic ops	13.9ms	13.7ms	1.02× ✅
nested loops 100×100	520µs	533µs	1.03× ✅
recursive fib(20)	870µs	526µs	0.60×
iterative fib(10k)	598µs	1733µs	2.90× ✅
string concat ×2000	106µs	161µs	1.52× ✅
list build+sum (500)	76µs	245µs	3.22× ✅
5k function calls	290µs	313µs	1.08× ✅
500 variable lookups	426µs	1596µs	3.75× ✅
20-deep nesting	18µs	80µs	4.44× ✅
heavy branching ×5000	376µs	385µs	1.02× ✅

Score: 9/10 benchmarks faster than CPython 3.12

Run python3 bench_cpython.py to reproduce CPython numbers on your machine.

Architecture

Source Code
    │
    ▼
┌─────────┐     ┌──────────┐     ┌──────────┐     ┌──────────────┐     ┌─────┐
│  Lexer  │────▶│  Parser  │────▶│   AST    │────▶│   Compiler   │────▶│ VM  │
│         │     │          │     │          │     │  + Peephole   │     │     │
└─────────┘     └──────────┘     └──────────┘     └──────────────┘     └─────┘
 token.rs        parser.rs        ast.rs          compiler.rs          vm.rs
 lexer.rs                                         bytecode.rs

See SPEC.md for detailed architecture and WIKI.md for the optimization journey.

Project Structure

src/
├── main.rs          # CLI entry point (REPL + file runner)
├── lib.rs           # Library crate root
├── token.rs         # Token enum and keyword mapping
├── lexer.rs         # Hand-rolled lexer with indent/dedent tracking
├── ast.rs           # AST node definitions (Expr, Stmt, BinOp, etc.)
├── parser.rs        # Recursive-descent parser
├── symbol.rs        # String interning (Symbol → u32)
├── bytecode.rs      # Op enum, CodeObject, Value, FunctionObj
├── compiler.rs      # AST → bytecode compiler + peephole optimizer
├── interpreter.rs   # Tree-walking interpreter (legacy, used by REPL)
├── vm.rs            # Bytecode virtual machine
└── bin/
    └── benchmark.rs # Performance benchmark suite
bench_cpython.py     # Equivalent CPython benchmarks for comparison

Example

def fib(n):
    if n <= 1:
        return n
    return fib(n - 1) + fib(n - 2)

print(fib(20))

$ viper fib.py
6765

Building

Requires Rust 2021 edition. Single dependency: rustc-hash.

cargo build --release

License

MIT