A way to capture the span of previous tokens in the error?

[filiptrplan]

So I have a rule that first matches a keyword, and then another parser with matches a list. If the list parser fails, it returns an error but only with the span of the tokens that should have been the list. So when I display the error, the initial keyword is not shown.

I currently just manually decrement the span by one when mapping the error, but I was wondering if I could somehow do this automatically / less error prone than just decrementing the span?

just(Token::KwAnd)
  .ignore_then(match_list.clone())
  .map_err(|err| {
      ParserError::MatchListAfterLogicalOperator(
          (err.span().start - 1..err.span().end).into(),
      )
  })
  .map(ParserMatcher::And)

[filiptrplan]

Leaving a solution for anyone that comes across this problem:

just(Token::KwAnd)
    .ignore_then(match_list.clone())
    .map_err_with_state(|err, span, _| {
        ParserError::MatchListAfterLogicalOperator(span.union(err.span()))
    })
    .map(ParserMatcher::And)