A Practical Example

We’re going to make a parser for a configuration file. That file contains the options to generate a parser with Lexigram.

There are currently two ways of setting the options when you generate a parser with Lexigram: the command-line options arguments and the option’s fluent methods used when generating the parser programmatically.

Here is an example of options to generate the little example discussed in the tutorial overview:

lexigram --indent 4 -c example.lg -l parser.rs tag example_lexer\
  -p parser.rs tag example_parser\
  --lib "super::user_types::*"  

And here is the equivalent if the parser is generated programmatically:

#![allow(unused)]
fn main() {
static GRAMMAR_FILENAME: &str = "example.lg";
static PARSER_FILENAME: &str = "parser.rs";
let options = OptionsBuilder::new()
    .indent(4)
    .combined_spec(genspec!(filename: GRAMMAR_FILENAME))
    .lexer_code(gencode!(filename: PARSER_FILENAME, tag: "example_lexer"))
    // grammar is combined with lexicon, no need to define parser_spec
    .parser_code(gencode!(filename: PARSER_FILENAME, tag: "example_parser"))
    .libs(["super::user_types::*"])
    .build()
    .expect("should have no error");
match try_gen_parser(action, options) {
    Ok(log) => {
        if action == Action::Generate {
            println!("Code generated");
        }
        assert!(
            log.has_no_warnings(),
            "unexpected warning(s):\n{}",
            log.get_warnings().join("\n"));
    }
    Err(build_error) => panic!("{build_error}"),
}
}

What we would like is a text-based input that specifies the same options, and which could be stored in a configuration file, or maybe combined with the lexicon and the grammar:

def GRAMMAR_FILENAME = "example.lg";
def PARSER_FILENAME = "parser.rs";
lexer {
    combined: GRAMMAR_FILENAME,
    output: PARSER_FILENAME ["example_lexer"]
}
parser {
    output: PARSER_FILENAME ["example_parser"]
}
options {
    libs: { "super::user_types::*" },    
    indent: 4
}