Method parseArgumentGroup

src/Parser.ts:776–802

* Parses an argument with the mode specified.

(optional: boolean, mode?: Mode)

     * Parses an argument with the mode specified.
     */
    parseArgumentGroup(optional: boolean, mode?: Mode): ParseNode<"ordgroup"> | null {
        const argToken = this.gullet.scanArgument(optional);
        if (argToken == null) {
            return null;
        }
        const outerMode = this.mode;
        if (mode) { // Switch to specified mode
            this.switchMode(mode);
        }

        this.gullet.beginGroup();
        const expression = this.parseExpression(false, "EOF");
        // TODO: find an alternative way to denote the end
        this.expect("EOF"); // expect the end of the argument
        this.gullet.endGroup();
        const result: ParseNode<"ordgroup"> = {
            type: "ordgroup",
            mode: this.mode,
            loc: argToken.loc,
            body: expression,
        };

        if (mode) { // Switch mode back
            this.switchMode(outerMode);
        }
        return result;
    }

    /**
     * Parses an ordinary group, which is either a single nucleus (like "x")