revising ev, was: problem with "concatting variables"

>>>>> "Stavros" == Stavros Macrakis <macrakis at alum.mit.edu> writes:

    Stavros> John, I think we all agree that Maxima should never give
    Stavros> a Lisp (internal)?error. ?That is always the wrong
    Stavros> behavior, and we should be fixing these things. A better
    Stavros> message in these cases would be: "Maxima encountered an
    Stavros> internal error. ?Please report exactly what caused this
    Stavros> to ...".

We should probably change that message.  I think that's easy
enough.  Do we still want to spam the use with the actual Lisp error?
I think that's useful information.

    Stavros> About having length("cat") => length("cat"), I don't
    Stavros> agree. ?That would mean that silly errors like

    Stavros> ? ? ? ? if length("cat")=3 then a else b

    Stavros> will return b. ?After all, the expression length("cat")
    Stavros> does not equal 3. That will be hell to debug, especially
    Stavros> for a beginning user.

Any reason not to extend length to work with strings?

Ray