Match a string with tokenizer only if it is first token in line

[dhowe]

When tokenizing, how to match a token only if it is the first thing in a line?

Take the following example where I am trying to match any ident followed by a colon, ONLY if it is the first thing in the line (thus the ^):

static TextParser<Unit> Actor { get; } =
  from start in Span.Regex(@"^[A-Za-z][A-Za-z0-9_]+:")
  select Unit.Value;

It seems that if the line is "1 abc:" and Ignore(Span.WhiteSpace) is set, then the tokenizer consumes the first token ('1'), then ignores the white space as directed, then sees "abc:" as starting from position 0, thus matching.

But what I want is to only match "abc:" if it is the first token ... Is this possible ?

[dhowe]

Posted here: https://stackoverflow.com/questions/53029386/superpower-match-a-string-with-tokenizer-only-if-it-begins-a-line, with code/tests

[AndrewSav]

It looks like the answer is given to you on StackOverflow. Basically it boils down to the fact that if TokenizerBuilder does not do what you want you need to build you Tokenizer yourself. Is there anything else with this question that is unresolved?