NEScript

A statically-typed, compiled programming language for NES game development.

NEScript compiles .ne source files directly into playable iNES ROM files, with no external assembler or linker dependencies. The compiler handles everything from source text to a ROM you can run in any NES emulator.

An end-to-end side-scrolling platformer compiled from a single .ne source file — custom CHR art, full background nametable with per-region palettes, physics-driven hero, scrolling camera, enemies, coins, user-declared SFX/music, and a Title → Playing state machine, all in 24 KB of 6502 code.

Quick Start

# Build the compiler
cargo build --release

# Compile an example
cargo run -- build examples/hello_sprite.ne

# Run the output ROM in an emulator
# (produces examples/hello_sprite.nes)

Hello World

game "Hello" {
    mapper: NROM
}

var px: u8 = 128
var py: u8 = 120

on frame {
    if button.right { px += 2 }
    if button.left  { px -= 2 }
    if button.down  { py += 2 }
    if button.up    { py -= 2 }

    draw Smiley at: (px, py)
}

start Main

Features

• Game-aware syntax -- states, sprites, palettes, backgrounds, and input are first-class constructs
• Full type system -- u8, i8, u16, bool, fixed-size arrays (u8[N]), enum, struct
• Rich control flow -- if/else, while, for i in 0..N, loop, match
• Functions -- with parameters, return types, inline hint, recursion detection
• State machines -- state with on enter, on exit, on frame, on scanline(N) handlers
• Compile-time safety -- call depth limits, recursion detection, type checking, unused-var warnings
• IR-based optimizer -- constant folding, dead code elimination, strength reduction (incl. div/mod by power-of-two), copy propagation, peephole passes including INC/DEC fold and live-range slot recycling
• Full 16-bit arithmetic -- u16 add/sub/compare lower to carry-propagating paired operations
• Multiple mappers -- NROM, MMC1, UxROM, MMC3 (including multi-scanline IRQ dispatch per state)
• Audio subsystem -- frame-walking pulse driver with user-declared sfx/music blocks, builtin effects and tracks, period table, and zero-cost elision when unused
• Palette & background pipeline -- palette and background blocks, initial values loaded at reset, vblank-safe set_palette / load_background runtime swaps
• Asset pipeline -- PNG-to-CHR conversion, inline tile data, sfx envelopes, music note streams
• Inline assembly -- asm { ... } with {var} substitution, plus raw asm { ... } for verbatim blocks
• Hardware intrinsics -- poke(addr, value) / peek(addr) for direct register access
• Debug support -- --debug flag enables debug.log / debug.assert writes to the emulator debug port
• Compile-time diagnostics -- --dump-ir, --memory-map, --call-graph flags
• Single binary -- no dependencies on ca65, Python, or any external tools

Documentation

• Language Guide -- complete reference for every language feature
• Architecture -- compiler internals and module overview
• NES Reference -- hardware quick reference for contributors
• Examples README -- how to build and run examples

Examples

Example	Features demonstrated
hello_sprite.ne	D-pad input, sprite drawing
bouncing_ball.ne	Automatic movement, edge detection
coin_cavern.ne	Multi-state game, functions, constants, gravity
arrays_and_functions.ne	Arrays, functions, while loops, inline functions
state_machine.ne	State transitions, on enter/exit, timers
sprites_and_palettes.ne	Inline CHR data, scroll, type casting
mmc1_banked.ne	MMC1 mapper, bank declarations, multiply
palette_and_background.ne	Palette and background declarations, reset-time load, vblank-safe set_palette / load_background swaps
structs_enums_for.ne	Structs, enums, for loops, struct literals
inline_asm_demo.ne	Inline asm with {var} substitution, poke/peek
audio_demo.ne	Audio subsystem: user sfx/music blocks, builtin effects, play/start_music/stop_music
platformer.ne	End-to-end side-scroller — custom CHR tileset, full background nametable, metasprite player with gravity/jump physics, wrap-around scrolling, enemies, coins, user-declared SFX + music, and a Title → Playing state machine with auto-play for the headless harness

Compiler Commands

# Compile to ROM
nescript build game.ne

# Compile with custom output path
nescript build game.ne --output my_game.nes

# Type-check only (no ROM output)
nescript check game.ne

# View generated 6502 assembly
nescript build game.ne --asm-dump

# Enable debug mode
nescript build game.ne --debug

Emulator Compatibility

Output ROMs are standard iNES format and work with any NES emulator:

• Mesen -- recommended, best debugging support
• FCEUX
• Nestopia

Project Status

NEScript implements all five planned milestones:

Milestone	Status	Key Features
M1: Hello Sprite	Done	Full compiler pipeline, assembler, ROM builder
M2: Game Loop	Done	Functions, arrays, IR, optimizer, call graph analysis
M3: Asset Pipeline	Done	PNG-to-CHR, sprites, debug.log / debug.assert
M4: Optimization	Done	Strength reduction, ZP promotion, type casting, asm-dump
M5: Bank Switching	Done	MMC1/UxROM/MMC3, bank declarations, software mul/div

497 tests across the lexer, parser, analyzer, IR, optimizer, codegen, assembler, linker, runtime, ROM, and asset modules, with CI running fmt, clippy, test, and example compilation on every push.

License

MIT