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
or
read_table_fields/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 order option
in new_table/4).
Options are:
prefix | Uses prefix search with the default
table. |
prefix(Table) | Uses prefix search
with the specified ordering table. |
substring | Searches for a substring in the
field. This requires linear search of the table. |
substring(Table) | Searches for a
substring, using the table information for determining the equivalence
of characters. |
= | Default equivalence. |
=(Table) | 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
unique set (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.dat table from the AAT
database used in GRASP
C1C2,Full Name
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)], _).
