Using whitespace as a list separator

Question

I can successfully parse a comma-delimited list with dart-petitparser, but the same code fails when confronted with a space-delimited list:

class MyDefinition extends GrammarDefinition {
  @override
  Parser start() => throw UnsupportedError('Not yet.');

  Parser commas() =>
      ref0(number).separatedBy(char(','), includeSeparators: false);
  Parser spaces() =>
      ref0(number).separatedBy(char(' '), includeSeparators: false);
  Parser<int> number() => digit().plus().flatten().trim().map(int.parse);
}

  test('commas', () {
    var defn = MyDefinition();
    var parser = defn.build(start: defn.commas);
    expect(parser.parse("7,4,9,5").value, [7, 4, 9, 5]);  // PASS
  });

  test('spaces', () {
    var defn = MyDefinition();
    var parser = defn.build(start: defn.spaces);
    expect(parser.parse("7  4 9    5").value, [7, 4, 9, 5]); // FAIL
  });

It fails with the following:

  Expected: [7, 4, 9, 5]
    Actual: [7]
     Which: at location [1] is [7] which shorter than expected

What am I doing wrong? I've dug through a bunch of the example grammars, and didn't find a whitespace-delimited list anywhere.

Answer 1

The .trim() parser in your number parser is consuming whitespaces before and after the number. This prevents the space-delimited list parser from finding a separating whitespace.

I suggest to rewrite as:

Parser spaces() =>
    ref0(number).separatedBy(char(' ').plus(), includeSeparators: false);
//                           add this ^^^^^^^
Parser<int> number() =>
    digit().plus().flatten().map(int.parse);
//        remove trim, here ^