private void RegisterPrefix(TokenType t, PrefixParseFn fn) => _prefixParseFns.Add(t, fn);
private void RegisterPrefix(TokenType tokenType, PrefixParseFn fn) { _prefixParseFn[tokenType] = fn; }
private void RegisterPrefix(TokenType tokenType, PrefixParseFn fn) { _prefixParseFns.Add(tokenType, fn); }