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Try-Except 执行扩展时

tag-icon • tag-icon expansion protected-macro
Try-Except 执行扩展时

是否可以编写一个函数来执行以下操作：

function \tryexpand (\foo):
    try:
         expand(\foo)
    except (Argument of \@following has an extra }):
         store "\relax" in `\result`
    else:
         store expansion of `\foo` in `\result`
    
    return \result

上下文：我正在尝试做\edef\result{\expandafter\empty\foo}（规避），如果不需要任何参数则\protect有效，否则会失败。\foo

测试用例

\newcommand{\needsthree}[3]{#3#2#1}
\protected\def\foo{\needsthree}
% --> \tryexpand{\foo} should lead to \result being macro:->\relax
\newcommand{\needsnone}{42}
\protected\def\bar{\needsnone}
% --> \tryexpand{\bar} should lead to \result being macro:->42

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