How to just trim left or right in PetitParserDart

Question

There is a trim() method which will create a parser to trim a string on both side.

How to create one which just trim the left or right?

Answer 1

The following helpers create parsers that trim in all possible ways:

Parser trim(Parser parser, [Parser trimmer]) {
  if (trimmer == null) trimmer = whitespace();
  return trimmer.star().seq(parser).seq(trimmer.star()).pick(1);
}

Parser trimRight(Parser parser, [Parser trimmer]) {
  if (trimmer == null) trimmer = whitespace();
  return parser.seq(trimmer.star()).pick(0);
}

Parser trimLeft(Parser parser, [Parser trimmer]) {
  if (trimmer == null) trimmer = whitespace();
  return trimmer.star().seq(parser).pick(1);
}

The above function trim results in an equivalent parser to the built-in function Parser.trim.