Ok, in lua it's indeed simple:

\startluacode
list = {"foo", "bar", "baz"}
\stopluacode

\starttext

\startluacode
for i, v in ipairs(list) do
    if i == #list then
        tex.print("last:")
        tex.print(v)
    elseif i == 1 then
        tex.print("first:")
        tex.print(v)
    else
        tex.print("in between:")
        tex.print(v)
    end
end
\stopluacode

\stoptext

But, it'd still love to hear whether there is a solution on the tex side.

Denis

Von: Maier, Denis Christian (UB)
Gesendet: Montag, 2. Mai 2022 09:15
An: 'mailing list for ConTeXt users' <ntg-context@ntg.nl>
Betreff: process list items differently depending on position in list

Hi,

I need to process a comma separated list, and adapt the formatting according to the position of an item in the list (example below). Expected output would be:
{\bf foo
}, {\em bar} and baz.

Is that possible? Can I somehow get the position of an item in the list? (My understanding is that \processcommalist and \processcommacommand apply a command to each list item, but there is no such thing as <position in the list>... I hope I'm wrong here.)

Or is that something where using Lua would be a better choice?

Best,
Denis

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\define[1]\command
  {#1}

\define\somelist
  {foo, bar, baz}

\starttext

  \processcommacommand
    [\somelist]
    \command

\stoptext
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%