private void RegisterInfix(TokenType t, InfixParseFn fn) => _infixParseFns.Add(t, fn);
private void RegisterInfix(TokenType tokenType, InfixParseFn fn) { _infixParseFn[tokenType] = fn; }
private void RegisterInfix(TokenType tokenType, InfixParseFn fn) { _infixParseFns.Add(tokenType, fn); }