// file:    mail4.rex
// author:  keller
// purpose: development of a mailing list processor, step 4

// select(lists, db) creates a list of individuals in the 
// mailing lists with no duplicates

select(lists, db) = 
  remove_duplicates(
    mappend(rest, keep((List) => member(first(List), lists), db)));


test() = select(["cs-majors", "math-majors", "class of 00"], db);


// built-in functions used: first, rest, member, keep, mappend, 
//                          remove_duplicates


// db is the database of mailing lists; It is a list of lists.
// Each list consists of the name of the mailing list, followed by
// the individuals on the list.

db = [
       ["cs-majors",       "mary",   "john",  "tom",   "avi"    ],
       ["math-majors",     "alice",  "tom",   "franz", "yukio"  ],
       ["class of 99",     "mary",   "tom",   "yukio"           ],
       ["class of 00",     "john",   "avi",   "alice", "franz"  ],
       ["cs-faculty",      "george", "gwen",  "prithi"          ], 
       ["math-faculty",    "al",     "gwen"                     ],
       ["curriculum-comm", "al",     "prithi"                   ]
     ];