[texhax] Composing two commands one inside another

[Rodolfo Medina]

Hi, all.

In plain TeX, I want to compose to commands together, one inside another.
I say, e.g.,
\edef\a#1,#2{#1} 
and
\edef\b#1{#1,dog};
then I want to define \c#1,#2 so that the value of \a is collected from \b:
so that \c{cat,mouse} should give the result 'cat,dog'.
I tried with
\edef\c#1,#2{\b{\a#1,#2}}, but it didn't work.

Please anyone who can help?
(Sorry for my ignorance!)
Thanks,
        Rodolfo