Grammar and parsing libraries for Rust

grmtools is a suite of Rust libraries and binaries for parsing text, both at compile-time, and run-time. Most users will probably be interested in the compile-time Yacc feature, which allows traditional

.y

Quickstart

A minimal example using this library consists of two files (in addition to the grammar and lexing definitions). First we need to create a file

build.rs

use cfgrammar::yacc::YaccKind;
use lrlex::CTLexerBuilder;

fn main() -> Result> {
    CTLexerBuilder::new()
        .lrpar_config(|ctp| {
            ctp.yacckind(YaccKind::Grmtools)
                .grammar_in_src_dir("calc.y")
                .unwrap()
        })
        .lexer_in_src_dir("calc.l")?
        .build()?;
    Ok(())
}

This will generate and compile a parser and lexer, where the definitions for the lexer can be found in

src/calc.l

%%
[0-9]+ "INT"
\+ "+"
\* "*"
\( "("
\) ")"
[\t ]+ ;

and where the definitions for the parser can be found in

src/calc.y

%start Expr
%avoid_insert "INT"
%%
Expr -> Result:
      Expr '+' Term { Ok($1? + $3?) }
    | Term { $1 }
    ;

Term -> Result:
      Term '*' Factor { Ok($1? * $3?) }
    | Factor { $1 }
    ;
Factor -> Result:
      '(' Expr ')' { $2 }
    | 'INT'
      {
          let v = $1.map_err(|_| ())?;
          parse_int($lexer.span_str(v.span()))
      }
    ;
%%
// Any functions here are in scope for all the grammar actions above.
fn parse_int(s: &str) -> Result {
    match s.parse::() {
        Ok(val) => Ok(val),
        Err(_) => {
            eprintln!("{} cannot be represented as a u64", s);
            Err(())
        }
    }
}

We can then use the generated lexer and parser within our

src/main.rs

use std::env;

use lrlex::lrlex_mod;
use lrpar::lrpar_mod;
// Using lrlex_mod! brings the lexer for calc.l into scope. By default the
// module name will be calc_l (i.e. the file name, minus any extensions,
// with a suffix of _l).
lrlex_mod!("calc.l");
// Using lrpar_mod! brings the parser for calc.y into scope. By default the
// module name will be calc_y (i.e. the file name, minus any extensions,
// with a suffix of _y).
lrpar_mod!("calc.y");
fn main() {
    // Get the LexerDef for the calc language.
    let lexerdef = calc_l::lexerdef();
    let args: Vec = env::args().collect();
    // Now we create a lexer with the lexer method with which we can lex an
    // input.
    let lexer = lexerdef.lexer(&args[1]);
    // Pass the lexer to the parser and lex and parse the input.
    let (res, errs) = calc_y::parse(&lexer);
    for e in errs {
        println!("{}", e.pp(&lexer, &calc_y::token_epp));
    }
    match res {
        Some(r) => println!("Result: {:?}", r),
        _ => eprintln!("Unable to evaluate expression.")
    }
}

For more information on how to use this library please refer to the grmtools book, which also includes a more detailed quickstart guide.

Examples

lrpar contains several examples on how to use the

lrpar

lrlex

Documentation

• grmtools book
• lrpar
• lrlex
• lrtable