>> \def\quark\quark{\quark}
>
> with error message "Use of \quark doesn't match its definition" if it's ever
> accidentally executed. I *think* this definition still fulfils the use case
> for quarks themselves, but I wonder if it would involve a little too much
> code shuffling to be worth implementing for expl3.
>
> (And it makes it more difficult to peek inside a quark, if that's ever
> necessary.)
>
> matter?

Hi Will,

if I understand correctly, quarks are meant to work in cases like

\def\foo{#1}
\ifx\foo\quark  ... \else ... \fi

This requires quarks to be defined as expanding to themselves.
Or it requires to distinguish between a quark and a token list containing
that quark.

I personally don't use quarks as anything else than delimiters, so any
definition is fine, but I guess that property of quarks is used in
constructions
like

\tl_set:Nn \foo {#1}
\quark_if_recursion_tail_stop:N \foo

or

\prop_get:NnN \foo {key} \bar
\quark_if_no_value:NTF \bar { } { }

This could be solved by altering quark tests, perhaps...?

Regards,
Bruno
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