iee - Icon expression evaluator

I've uploaded a new version of my Icon expression evaluator, changing
the name to reflect a mayor change in the results of evaluation
given.  Now 'fail' and 'return' return 'Failed.' and '&null'
respectively, reflecting what is actually returned by procedures when
these functions are used.  Likewise, an identifier that has not been
assigned a value fails instead of returning '&null', and values that
are not explicitly returned fail ( '3 + 4'  fails, while 'return 3 +
4' returns 7 ).
Otherwise, it is the same program, available at:
http://www.costarricense.cr/pagina/ernobe/iee.txt