.rs

// I have to create a custom type because the undesired behavior
// only occurs if I use a custom type for the parsing result. If
// I tried with something like bool, I get my custom error returned
// back just as I want it. Very strange.
pub enum MyUnit { Only }

// Now this parser returns "found end of input" if the input is not
// equal to "only". But a custom error is generated and wanted to be
// returned instead.
pub fn example() -> impl Parser<char, MyUnit, Error = Simple<char>> {
    text::ident().padded()
        .try_map(|s: String, span| {
            match s.as_str() {
                "only" => Ok(MyUnit::Only),
                _ => Err(Simple::custom(span, format!("invalid bool value {:?}", s))),
            }
        })
}