parsergen-backend-rust.md

Parser Generator Backend: Rust

This backend outputs a parser as Rust source code. See parser generator backends for what every generated parser does and scanner generator backend: Rust for the scanner side.

The output is a module which needs nothing beyond the standard library, and puts no constraint on the edition of the crate it is dropped into.

--backend-rust-scanner-module sets the module path the token type and the token source trait are taken from, which defaults to super::scanner.

Parser::parse takes anything implementing TokenSource and returns a ParseResult holding the tree and the errors, and can be called again with another scanner. The tree is None when the parse could not be finished. The result is #[must_use], since dropping it unlooked at drops every error the parse reported. Lexemes borrow from the source, so the borrow checker enforces that the source outlives the tree.

Example

examples/calculator/rust/ is a calculator built on this backend. Its parser was generated with:

golr parser \
  --frontend golr \
  --frontend-file-path calculator.golr \
  --backend rust \
  --backend-file-path src/parser/parser.rs