Source : Free On-Line Dictionary of Computing

XPOP
     
         An extensible {macro assembly} language with
        user-redefinable {grammar}, for use with {FAP}.
     
        ["XPOP: A Meta-language Without Metaphysics", M.I. Halpern,
        Proc FJCC 25:57-68, AFIPS (Fall 1964)].
     
        (1995-04-28)