- in_table(+Handle, ?Fields, -RecordPos)
- Searches the table for records matching Fields. If a match is
found, the variable (see below) fields in Fields are unified
with the corresponding field value, and RecordPos is unified
with the position of the record. The latter handle may be used in a
subsequent call to read_table_record/4
Fields is a list of field specifiers. Each specifier is of the format:
FieldName(Value [, Options])
Options is a list of options to specify the search. By default, the package will search for an exact match, possibly using the ordering table associated with the field (see
orderoption in new_table/4). Options are:
Uses prefix search with the default table.
Uses prefix search with the specified ordering table.
Searches for a substring in the field. This requires linear search of the table.
Searches for a substring, using the table information for determining the equivalence of characters.
Equivalence using the given table.
If Value is unbound (i.e. a variable), the record is considered not specified. The possible option list is ignored. If a match is found on the remaining fields, the variable is unified with the value found in the field.
First, the system checks whether there is an ordered field that is specified. In this case, binary search is employed to find the matching record(s). Otherwise, linear search is used.
If the match contains a specified field that has the property
uniqueset (see new_table/4), in_table/3 succeeds deterministically. Otherwise it will create a backtrack-point and backtracking will yield further solutions to the query.
in_table/3 may be comfortable used to bind the table transparently to a predicate. For example, we have a file with lines of the format.1This is the
disproot.dattable from the AAT database used in GRASP
C1C2 is a two-character identifier used in the other tables, and FullName is the description of the identifier. We want to have a predicate identifier_name(?Id, ?FullName) to reflect this table. The code below does the trick:
:- dynamic stored_idtable_handle/1. idtable(Handle) :- stored_idtable_handle(Handle). idtable(Handle) :- new_table('disproot.dat', [ id(atom, [downcase, sorted, unique]), name(atom) ], [ field_separator(0',) ], Handle), assert(stored_idtable_handle(Handle)). identifier_name(Id, Name) :- idtable(Handle), in_table(Handle, [id(Id), name(Name)], _).