sexp type checking

[Roland Winkler]

For BBDB I'd like to have a function for checking recursively the
type of a sexp, similar to what customize is doing via its :type
argument. The function should throw a mismatch error if the type
checking fails.

I do not want to reinvent the wheel. Does such a function already
exist? (Where??) If not, would it possibly be useful elsewhere, too?

I also looked into the customize code whether it contained something
that I could use for my purposes. Yet I do not know much about this
code. If it could be used to define such a function, I'd much
appreciate some hints how this can be done.

Thanks,

Roland