After ideas.  Given:

LIST=one two
LIST+= three

how does one output one,two,three or one|two|three
since make insists on separating the words with space.
Assume that ${LIST} is used for various things such that at times the
space separation is desired and other times it isn't.

One can of course:

    @x=`echo ${LIST} | tr ' ' '|'`; echo $$x

but that's rather limited.

I suspect the solution is to provide a modifier that defines the
separator to use, or a modifier that allows one to a regexp
substitution on the expanded buffer.

Other options?

Thanks
--sjg