Demo different parser styles

demo_parser_styles.ts

// This is what imperative style looks like when the parser is
// implemented with exceptions for control flow
function imperative_style_with_exceptions(p: Parser) {
    p.consume('look at'); // could throw NoMatch

    let who = p.split([ // could throw Split or NoMatch
        () => p.consume('me', 'me'),
        () => p.consume('mewtwo', 'mewtwo'),
        () => p.consume('steven', 'steven'),
        () => p.consume('martha', 'martha')
    ]);

    if (who === 'steven') {
        p.eliminate(); // throws NoMatch
    }

    let how = p.split([ // could throw Split or NoMatch
        () => p.consume('happily', 'happily'),
        () => p.consume('sadly', 'sadly'),
        () => 'neutrally'
    ]);

    p.submit(); // could throw NoMatch

    return `You looked at ${who} ${how}`;
}

// This is what imperative style looks like when the parser is
// implemented with explicit early returns
function imperative_style_with_explicit_early_returns(p: Parser) {
    let _ = p.consume('look at'); // could return NoMatch
    if (parse_failed(_)) {
        return _
    }

    let who = p.split([ // could return Split or NoMatch
        () => p.consume('me', 'me'),
        () => p.consume('mewtwo', 'mewtwo'),
        () => p.consume('steven', 'steven'),
        () => p.consume('martha', 'martha')
    ]);
    if (parse_failed(who)) {
        return who;
    }

    if (who === 'steven') {
        return p.eliminate(); // returns NoMatch
    }

    let how = p.split([ // could returns Split or NoMatch
        () => p.consume('happily', 'happily'),
        () => p.consume('sadly', 'sadly'),
        () => 'neutrally'
    ]);
    if (parse_failed(how)) {
        return how;
    }

    _ = p.submit(); // could return NoMatch
    if (parse_failed(_)) {
        return _;
    }

    return `You looked at ${who} ${how}`;
}


// This is what functional style looks like regardless of the implementation
const functional_style = ((p: Parser) =>
    p.consume('look at', () =>

    p.split([
        () => p.consume('me', 'me'),
        () => p.consume('mewtwo', 'mewtwo'),
        () => p.consume('steven', 'steven'),
        () => p.consume('martha', 'martha')
    ], (who) => 

    who === 'steven'
        ? p.eliminate() :

    p.split([
        () => p.consume('happily', 'happily'),
        () => p.consume('sadly', 'sadly'),
        () => 'neutrally'
    ], (how) =>

    p.submit(() =>

    `You looked at ${who} ${how}`
)))));

let command = raw('look at me');

// Run them using
Parser.run_thread(command, imperative_style_with_exceptions);
Parser.run_thread(command, imperative_style_with_explicit_early_returns);
Parser.run_thread(command, functional_style);