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HELP FOREVERY                                           AS JLC, July 1982

This is used for selective iteration over a database. The formats of

    forevery <list of patterns> do <actions> endforevery;
    forevery <list of patterns> in <database> do <actions> endforevery;

When 'in <database>' is omitted, then the value of the POP-11 variable
DATABASE is used as the database (see HELP *DATABASE).

FOREVERY is a generalization of *FOREACH. FOREVERY is to *ALLPRESENT as

FOREVERY tries to find (almost) every possible way of matching (see HELP
*MATCHES) the list of patterns against the database. For each such match,
FOREVERY produces an instantiation of the list of <patterns> and assigns it
to the variable THEM, which may be used inside <actions>. Here is a simple
example of the use of FOREVERY:

     vars database;
       [1 ison 2] [2 ison 3]
       [a ison b][b ison c] [d ison e] [e ison f] [g ison h] [a ison i]
         -> database;

     vars x,y,z;

     forevery [[?x ison ?y:isword][?y ison ?z]] do
         them =>
         [^x is above ^z] =>

     ** [[a ison b] [b ison c]]
     ** [a is above c]
     ** [[d ison e] [e ison f]]
     ** [d is above f]

     forevery [[??x ison ?y:isword][?y ison ??z]] do
         them =>
         [^x is above ^z] =>
     ** [[a ison b] [b ison c]]
     ** [[a] is above [c]]
     ** [[d ison e] [e ison f]]
     ** [[d] is above [f]]

Warning: if the list of patterns contains a pattern with ??, capable of
matching the same database item in different ways, then FOREVERY will only
find one way of matching the pattern with that item. E.g.

    [[c a b b a g e]] -> database;
    forevery [[??x b ??y]] do ....

This will not first match the "b" in the pattern to the first "b" in the
database, then match it to the second "b" (though the matcher may one day be
extended to allow this).

    *DATABASE - for use of the POP-11 database
    *FOR      - Iteration over lists and integers
    *FOREACH  - Selective iteration over a database by matching a pattern
    *WHICH    - uses FOREVERY to instantiate variables from a database
    *LOOPS    - for other types of iteration