pyparsing-rust

Stage-1 Rust mirror of pyparsing/pyparsing (pyparsing 3.3.3, MIT): a runtime-constructible grammar API for Python.

Boundary

The text-scan hot path — the remainder loops of CharsNotIn.parseImpl and White.parseImpl — lives in the reusable pyparsing-rust-core crate (no Python dependency) with a thin PyO3 binding (pyparsing._pyparsing). Everything else is the upstream source verbatim:

• ported to Rust: CharsNotIn / White scan loops (code-point exact, including lone surrogates);
• kept in Python: ParserElement dispatch (_parseNoCache), preParse whitespace skipping (FFI floor exceeds 1–3-char skips; measured), Word/Regex/Literal (already C-speed via re), ParseResults, SkipTo, helpers, common, testing, unicode, diagram, tools.

pyparsing/ keeps the exact public interface; when the compiled extension is absent the shims fall back to the upstream Python loops, so the tree also imports without a build.

Build

python3 -m venv .venv && . .venv/bin/activate
pip install maturin
maturin develop --release
python3 -m pytest tests/ -q

Layout

• pyparsing-core/ — reusable Rust core (pyparsing-rust-core on crates.io).
• src/lib.rs — PyO3 binding (pyparsing._pyparsing).
• pyparsing/core.py — upstream 3.3.3 plus two delegating parseImpl methods (diff against upstream shows only the delegation).
• tests/ — upstream suite (frozen oracle; do not weaken).

Measured performance

No accepted optimizations yet (mirror baseline); re-run release-prep after run --stage optimize merges winners. Artifact hashes are intentionally absent here; see release-manifest.json.