If I understand it correctly, you may need something like this...?

% Protection is key
\protected\def\inner[#1]{\empty}
% \outer is (or was) already defined in \CONTEXT
% Please use another name
\def\Outer{\inner[123] and \inner[some text] etc.}
\startluacode
local implement = interfaces.implement
local argument = tokens.scanners.argument
local function parseinner()
  local r = {}
  local str = argument()
  str = str:gsub("\\inner%s*(%b[])",function(s)r[#r+1] = s:sub(2,#s-1)end)
  context(table.concat(r," ")) -- Change " " by another spacer if needed
end
implement{name = "parseinner", public = true, actions = parseinner}
\stopluacode
\starttext
\parseinner{\Outer}
\stoptext

However, this will only work with very simple cases (no nesting, etc.).
Hope this helps.

Best regards,

Jairo

El mar, 16 de nov. de 2021 a la(s) 14:22, Joey McCollum via ntg-context (
ntg-context@ntg.nl) escribió:

> As the subject of this question suggests, this is really more of a
> question about expansion control (a topic that is still a bit obscure to
> me). Suppose I have a macro \inner that expects a single argument or an
> assignment of parameters in brackets. For my purposes, I don't want this
> macro to do anything when it is typeset, so I'll just define it as empty:
>
> ```
> \def\inner[#1]\empty
> ```
>
> Now suppose I have another macro \outer that invokes this macro with some
> specific input and sets some plain text after it:
>
> ```
> \def\outer{\inner[123] etc.}
> ```
>
> What I'd like to do is parse the argument of \inner in \outer. I was
> hoping that a string search in Lua would work, but I'm not having any luck.
> A minimal (non)-working example is included below:
>
> ```
>
> \def\inner[#1]\empty
>
> \def\outer{\inner[123] etc.}
>
>
> \startluacode
>
> local userdata = userdata or {}
>
> function userdata.parseinner(str)
>
> local innerparams = ""
>
>     if string.find(str, "\\inner(%b[])") then
>
>       i, j = string.find(str, "\\inner(%b[])")
>
>       innerparams = string.sub(str, i+1, j-1) -- we just want the content
> inside the brackets
>
>     end
>
>     context(innerparams)
>
>     return
>
> end
>
> \stopluacode
>
> \def\parseinner#1{\ctxlua{userdata.parseinner([==[#1]==])}}
>
>
> \starttext
>
> Testing:\blank
>
> \parseinner{\outer}
>
> \stoptext
> ```
>
> My problem is that when I pass \outer to the \parseinner macro, it gets
> fully expanded, so there isn't anything left to match "\\inner%b[]". Is
> there a way to expand \outer when I pass it to the \parseinner macro
> without also expanding the \inner macro inside it? Or is there some other
> preferred way of doing this?
>
> Joey
>
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