Quick start on ANTLR4 in Rust - part2

This is my note in adopting and learning ANTLR4Rust

Series

In the previous article, we built the minimal working example walking a parse tree using a listener. In this article, we are going to store a parsed CSV structure into a variable to use in the future.

Define a CSV structure:

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type Row = Vec<String>;#[derive(Debug)]
struct CSV {
    header: Row,
    rows: Vec<Row>,
}

Add fields to a listener:

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struct Listener {
    csv: Box<CSV>,
    add_to_header: bool,
    row_to_add: Vec<String>,
}

csv will be a resultant CSV structure. add_to_header and row_to_add are internal state variables to generate a CSV structure.

Implement a listener:

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impl CSVListener for Listener {
    fn enter_csvFile(&mut self, _ctx: &CsvFileContext) {}
    fn exit_csvFile(&mut self, _ctx: &CsvFileContext) {}
    fn enter_hdr(&mut self, _ctx: &HdrContext) {
        self.add_to_header = true;
    }
    fn exit_hdr(&mut self, _ctx: &HdrContext) {
        self.csv.header = self.row_to_add.to_vec();
        self.row_to_add.clear();
        self.add_to_header = false;
    }
    fn enter_row(&mut self, _ctx: &RowContext) {}
    fn exit_row(&mut self, _ctx: &RowContext) {
        if self.add_to_header {
            return;
        }
        self.csv.rows.push(self.row_to_add.to_vec());
        self.row_to_add.clear();
    }
    fn enter_field(&mut self, _ctx: &FieldContext) {}
    fn exit_field(&mut self, _ctx: &FieldContext) {
        self.row_to_add.push(_ctx.get_text());
    }
}

Feed an input to a parse and extract the result:

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fn main() {
    let input = String::from(
        "This, is, a, header
This, is, a, row
",
    );
    let lexer = CSVLexer::new(Box::new(InputStream::new(input)));
    let token_source = CommonTokenStream::new(lexer);
    let mut parser = CSVParser::new(Box::new(token_source));
    let listener_id = parser.add_parse_listener(Box::new(Listener {
        csv: Box::new(CSV {
            header: Row::new(),
            rows: Vec::new(),
        }),
        add_to_header: false,
        row_to_add: Row::new(),
    }));
    let result = parser.csvFile();
    assert!(result.is_ok());
    let listener = parser.remove_parse_listener(listener_id);
    let csv = listener.csv;
    println!("{:#?}", csv);
}

A tricky part is that we have to extract csv from listener. And to this end, we have to extract listener with listener_id.

The minimal working example can be found here.