grammar-kit

grammar-kit is the runtime support library for parsers generated by syn-grammar. It provides essential utilities for backtracking, error recovery, and testing syn-based parsers.

Features

1. Speculative Parsing (Backtracking)

The attempt function allows parsers to try a parsing branch and revert the stream cursor if it fails, without consuming tokens. This enables LL(k) lookahead and backtracking logic.

2. Intelligent Error Reporting

grammar-kit implements a "Deepest Error" heuristic. When multiple parsing branches fail, it preserves the error that occurred furthest into the token stream. This prevents generic "unexpected token" errors at the start of a block when a specific syntax error occurred deep inside it.

3. Testing Framework

The testing module provides a fluent API for unit testing your parsers.

Installation

Add this to your Cargo.toml:

[dependencies]
grammar-kit = "0.4.0"

Runtime Helpers

The library exposes several helper functions used by generated parsers:

• attempt: Forks the input, runs a closure, and advances only on success.
• parse_ident: Parses identifiers, accepting Rust keywords (via IdentExt).
• parse_int: Parses integer literals into typed Rust integers.
• skip_until: Skips tokens until a specific condition is met (used for error recovery).