Hello,

> Can someone show me or point me to some code where the peek functions
> have been used (preferably in a straightforward way)? I'm thinking in
> particular of functions like \peek_charcode:NTF.

Two packages seem to use these peek functions a lot: mhchem and
pkgloader.  One thing I note is that both packages involve
constructions reminiscent of a case statement:

    \peek_charcode:NTF M
      {
        \mypkg_grab_M_and_do_something:n
      }
      {
        \peek_charcode:NTF C
          {
            \mypkg_grab_C_and_do_something:n
          }
          {
            \mypkg_something_else:
          }
      }

Such code may be simplified (and sped up a bit) if we provided a
\peek_case_charcode:NnTF function.  Is there interest for such an
additional function?

Actually, looking at mhchem a bit more, it seems that there is
probably room for simplification if we provided better tools for
parsing.  I'll think.

Regards,

Bruno