fn trivial(token: Token) -> Option<TokenTree> {
        let token = match token {
            Token::Iden(iden) => TokenTree::Iden(iden),
            Token::Label(label) => TokenTree::Label(label),
            Token::Op(op) => TokenTree::Op(op),
            Token::Lit(lit) => TokenTree::Lit(lit),
            _ => panic!(),
        };

        Some(token)
    }
Performs a trivial identity conversion.
If the conversion is not trivial, this returns None.
Yes, I know this is opaque.
I plan to refactor this out eventually.
passerine/src/compiler/read.rs