Functions are Parsers!

With our Parser trait in place we can start implementing it. Thinking about the trait one implementation springs to mind.

If we have a function, or a lambda expression for that matter, that has the right signature. I.e. accepts a &str and returns a Result<(T, &str), ParseError>, in some sense it is a parser. We just have to apply the function!

Let's start with that implementation.

impl <'a, T, F> Parser<'a, T> for F where F: Fn(&'a str) -> Result<(T, &'a str), ParseError> {
    fn parse(&self, input: &'a str) -> Result<(T, &'a str), ParseError> {
        self(input)
    }
}

Exercises

1. Write the implementation of the Parser trait for Fn(&'a str) -> Result<(T, &'a str), ParserError>.