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nescript/examples
Claude fdb1ec7c91
cleanup: fix silent miscompiles and delete dead code exposed by code review
Two correctness bugs were silently producing wrong ROMs:

  - `x << n` / `x >> n` always shifted by 1, regardless of `n`, because
    the IR lowering for `BinOp::ShiftLeft`/`ShiftRight` hardcoded the
    count. Now eval_const the RHS into a compile-time count; fall back
    to a new `IrOp::ShiftLeftVar` / `ShiftRightVar` (runtime loop) when
    the amount isn't constant. Strength reduction folds the variable
    form back to a fixed count once the optimizer knows the value.

  - `x / n` / `x % n` always returned 0, because the lowering emitted
    `LoadImm(t, 0)` for `BinOp::Div`/`Mod` with a comment saying the
    runtime call was "TODO for now". Added real `IrOp::Div` and
    `IrOp::Mod`, wired them through use-counting and DCE, gave codegen
    `__divide`-based implementations, and taught strength reduction to
    rewrite power-of-two divisors into shifts and modulo-by-2ⁿ into
    AND masks. Constant folding now handles `Mul`/`Div`/`Mod`/shifts
    too, which were previously left for the codegen to emit inefficient
    software calls.

Dead code removed (no backward-compat shims kept):

  - `src/debug/` entirely. `DebugSymbols`, `SourceMap`, and the
    Mesen/.sym emitters had no callers outside their own tests;
    `main.rs` never wrote a symbol file. Documented the intent in
    `docs/future-work.md` so it comes back intentionally if needed.
  - `ErrorCode::E0202` (invalid cast) and `E0403` (unreachable state):
    defined, formatted, and marked `#[allow(dead_code)]` but never
    emitted. W0104 now carries the unreachable-state semantics too.
  - `Level::Info`: never constructed.
  - `load_background` / `set_palette` statements and their
    `BackgroundDecl` / `PaletteDecl` parser support: parsed and
    silently dropped by IR lowering (`// TODO: implement in asset
    pipeline`). Removed keywords, AST variants, parser paths, analyzer
    arms, and tests. `docs/future-work.md` documents the runtime
    palette/nametable design for when it comes back.

Doc cleanup:

  - `docs/architecture.md` was describing files that don't exist
    (`analyzer/types.rs`, `optimizer/const_fold.rs`, `codegen/regalloc.rs`,
    `rom/header.rs`, `debug/symbols.rs`, …). Rewrote it to match the
    real flat `mod.rs` + `tests.rs` layout and the real pipeline order.
  - `docs/future-work.md` was a hybrid of open work and "recently
    completed" entries that duplicated the active stubs at the top of
    the file. Collapsed to just the gaps that are actually still open.
  - `README.md` claimed Mesen symbol export and 210 tests; updated both.
  - `docs/language-guide.md` and `spec.md` described `palette` decls,
    `set_palette` / `load_background`, `debug.overlay`, and error codes
    that were never emitted. Trimmed.
  - Stale comments on `Statement::Play`/`StartMusic`/`StopMusic`
    claimed the audio subsystem was "a no-op at codegen time".

Tests:

  - Regression tests for every fix above (`lower_shift_left_with_literal
    _count_uses_that_count`, `lower_shift_right_with_variable_count
    _uses_runtime_variant`, `lower_divide_emits_div_op_not_load_imm
    _zero`, `lower_modulo_emits_mod_op_not_load_imm_zero`,
    `strength_reduce_div_by_power_of_two`, `strength_reduce_mod_by
    _power_of_two`, `strength_reduce_shift_var_with_constant_amount`).
  - Renamed the `program_with_sprites_and_palette` integration test
    (which was exercising the now-removed `load_background`/`set_palette`)
    to `program_with_inline_sprite_chr`.

`examples/sprites_and_palettes.ne` lost its `palette`/`set_palette`
usage. Nothing in the emulator test presses A, so the headless
jsnes render shouldn't move, but the golden may need regeneration
via `UPDATE_GOLDENS=1` if it does.

https://claude.ai/code/session_012fKB251HvEUQwG3tizFyqt
2026-04-13 02:47:37 +00:00
..
arrays_and_functions.ne Add README, LICENSE, examples, fix draw parser lookahead 2026-04-12 00:38:19 +00:00
audio_demo.ne audio: complete the subsystem — asset pipeline, user decls, tracker-style driver 2026-04-13 01:10:21 +00:00
bitwise_ops.ne examples: add 5 new programs covering match/loop/logic/bitwise/scanline 2026-04-12 19:05:18 +00:00
bouncing_ball.ne Add example builds to CI, document sprite name behavior 2026-04-11 22:55:43 +00:00
coin_cavern.ne M2: Wire IR pipeline, add Coin Cavern example and integration tests 2026-04-11 23:34:35 +00:00
comparisons.ne examples: 4 new programs covering MMC3 + other e2e gaps 2026-04-12 20:48:31 +00:00
function_chain.ne examples: 4 new programs covering MMC3 + other e2e gaps 2026-04-12 20:48:31 +00:00
hello_sprite.ne Add example builds to CI, document sprite name behavior 2026-04-11 22:55:43 +00:00
inline_asm_demo.ne examples: inline_asm_demo.ne 2026-04-12 18:02:59 +00:00
logic_ops.ne examples: add 5 new programs covering match/loop/logic/bitwise/scanline 2026-04-12 19:05:18 +00:00
loop_break_continue.ne examples: add 5 new programs covering match/loop/logic/bitwise/scanline 2026-04-12 19:05:18 +00:00
match_demo.ne examples: add 5 new programs covering match/loop/logic/bitwise/scanline 2026-04-12 19:05:18 +00:00
mmc1_banked.ne Add README, LICENSE, examples, fix draw parser lookahead 2026-04-12 00:38:19 +00:00
mmc3_per_state_split.ne examples: 4 new programs covering MMC3 + other e2e gaps 2026-04-12 20:48:31 +00:00
README.md cleanup: fix silent miscompiles and delete dead code exposed by code review 2026-04-13 02:47:37 +00:00
scanline_split.ne examples: add 5 new programs covering match/loop/logic/bitwise/scanline 2026-04-12 19:05:18 +00:00
sprites_and_palettes.ne cleanup: fix silent miscompiles and delete dead code exposed by code review 2026-04-13 02:47:37 +00:00
state_machine.ne Add README, LICENSE, examples, fix draw parser lookahead 2026-04-12 00:38:19 +00:00
structs_enums_for.ne Language: struct literals 2026-04-12 17:15:57 +00:00
two_player.ne examples: 4 new programs covering MMC3 + other e2e gaps 2026-04-12 20:48:31 +00:00
uxrom_banked.ne examples: add uxrom_banked and jsnes golden 2026-04-13 02:04:25 +00:00

NEScript Examples

Quick Start

# Build the compiler
cargo build --release

# Compile all examples
for f in examples/*.ne; do cargo run -- build "$f"; done

# Or compile one
cargo run -- build examples/hello_sprite.ne

Open any .nes file in an NES emulator (Mesen, FCEUX, etc.)

Examples

File Features Description
hello_sprite.ne input, draw Move a sprite with the d-pad
bouncing_ball.ne if/else, variables Auto-bouncing sprite with edge detection
coin_cavern.ne states, functions, constants 3-state game with gravity and coin collection
arrays_and_functions.ne arrays, functions, while Enemy array with collision detection
state_machine.ne on enter/exit, transitions Multi-state flow with timers
sprites_and_palettes.ne sprites, scroll, cast Inline CHR data, PPU scroll writes, type casting
mmc1_banked.ne MMC1, banks, multiply Banked mapper with software multiply

Emulator Controls

NES Button Typical Key
D-pad Arrow keys
A Z
B X
Start Enter
Select Right Shift

About Sprites

Sprite names in draw Player at: (x, y) are parsed and recorded in the AST. You can define sprites with inline CHR tile data:

sprite Player {
    chr: [0x3C, 0x42, 0x81, 0x81, 0x81, 0x81, 0x42, 0x3C,
          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
}

If no matching sprite declaration exists, the draw uses the built-in default tile (a smiley face). See sprites_and_palettes.ne for a full example.

Compiler Commands

# Compile to ROM
cargo run -- build game.ne

# Custom output path
cargo run -- build game.ne --output my_game.nes

# Type-check only
cargo run -- check game.ne

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

# Debug mode
cargo run -- build game.ne --debug