John Gibson Jan 1996
COPYRIGHT University of Sussex 1996. All Rights Reserved.
Select headings to return to index
database is a global permanent variable containing a list, used by the procedures described in this file (and also by the looping constructs for ... equalto and for ... allequalto, see HELP * equalto, HELP * allequalto).
All the procedures except database_add and database_alladd take a pattern or pattern_list as argument, and use the operator = to match database items against their argument. Consequently, any matchvars in pattern or pattern_list will have their corresponding variables set by the match. (For a description of matchvars, see Pattern Matching With = in HELP * EQUAL.)
(Note that this is primarily a teaching tool, so the database is stored as a simple list of items without any complicated indexing mechanism.)
Adds item to database (and also assigns item to database_it). item must not contain any matchvars (otherwise the mishap 'ADDING UNDER-SPECIFIED ITEM TO DATABASE' results).
Uses database_add to add each item in item_list to database (and also assigns a copy of item_list to database_them.)
Removes the first item in database that equals pattern (and assigns that item to database_it). If no matching item is found, the mishap 'REMOVING NON-EXISTENT ITEM FROM DATABASE' occurs.
Removes all items in database that equal pattern (and assigns a list of those items to database_them). It is permissible for no items to match (in which case database_them will be ).
Applies database_remove to each pattern in pattern_list to remove the first item in database that equals that pattern. A list of all items removed is assigned to database_them.
If there is an item in database that equals pattern, assigns that item to database_it. Otherwise, the mishap 'DATABASE LOOKUP FAILED' occurs.
database_present(pattern) -> bool [procedure]
If there is an item in database that equals pattern, assigns that item to database_it and returns true. Otherwise, returns false.
Note that if there is more than one item that equals pattern, database_present will find only the first possibility. The syntax form for ... equalto can be used to iterate through all possibilities (see HELP * equalto).
database_allpresent(pattern_list) -> bool [procedure]
Takes a list of patterns and returns true if there is at least one consistent way of matching all of them against items in database. (That is, not only must each pattern equal an item in database, but any matchvars bound must have the same values across all patterns.) If a consistent match can be found, a list of the database items matched is assigned to database_them, and true is returned; otherwise, false is returned.
Note that if there is more than one possible way of matching pattern_list, database_allpresent will find only the first possibility. The syntax form for ... allequalto can be used to iterate through all possibilities (see HELP * allequalto).
pattern present_in list -> bool [operator 5]
An operator version of database_present which allows any list to be used locally as database. This operator is just defined as
define 5 pattern present_in database; dlocal database; database_present(pattern) enddefine;
pattern_list allpresent_in list -> bool [operator 5]
An operator version of database_allpresent which allows any list to be used locally as database. This operator is just defined as
define 5 pattern_list allpresent_in database; dlocal database; database_allpresent(pattern_list) enddefine;
database_which(variables, pattern_list) -> value_list [procedure]
Using the for ... allequalto syntax form, this procedure finds all possible ways of consistently matching the patterns in pattern_list against items in database, and returns the values of either one variable, or a set of variables, for each possible match.
variables may be either (a) a single variable (i.e. an identifier or a word), or (b) a list of them. The resulting value_list is then for (a) a list of single variable values, or for (b) a list of lists of values.
database -> list [variable]
list -> database
The variable used by the procedures in this file to store a list of items.
database_it -> item [variable]
item -> database_it
This variable is used by various database procedures to store the last item operated on:
database_add and database_alladd set it to the last item added to database. database_remove, database_flush and database_allremove set it to the last item removed. database_lookup, database_present and present_in set it to the item matched from database.
database_them -> list [variable]
list -> database_them
This variable is used by various database procedures to store a list of the last set of items operated on:
database_alladd sets it to a copy of the last list of items added to database. database_allremove and database_flush set it to a list of the items removed. database_allpresent and allpresent_in set it to a list of the items matched from database.
--- C.all/ref/database --- Copyright University of Sussex 1996. All rights reserved.