Rich,

 | As others have said, these functions are not in the standard library.
 | However, useful functions like these[1] are available in 
 | Extlib, which you can find here:
 | 
 | http://sourceforge.net/projects/ocaml-lib/

Thanks. 

I don't understand why such functions are not part of the standard library.
Even if they are very easy to write, they are the kind of functions most
anyone _will_ have to write and not having them in the library is
inefficient.

Talking about efficiency, I've seen the solutions that have been posted, and
MHO is that having to recur to procedural constructs for such oviously
functional tasks as "implode" and "explode" seems odd.

Juanco