- Reference manual
- The SWI-Prolog library
- library(aggregate): Aggregation operators on backtrackable predicates
- library(apply): Apply predicates on a list
- library(assoc): Association lists
- library(broadcast): Broadcast and receive event notifications
- library(charsio): I/O on Lists of Character Codes
- library(check): Consistency checking
- library(clpb): CLP(B): Constraint Logic Programming over Boolean Variables
- library(clpfd): CLP(FD): Constraint Logic Programming over Finite Domains
- library(clpqr): Constraint Logic Programming over Rationals and Reals
- library(csv): Process CSV (Comma-Separated Values) data
- library(debug): Print debug messages and test assertions
- library(error): Error generating support
- library(gensym): Generate unique identifiers
- library(iostream): Utilities to deal with streams
- library(lists): List Manipulation
- library(main): Provide entry point for scripts
- library(nb_set): Non-backtrackable set
- library(www_browser): Activating your Web-browser
- library(option): Option list processing
- library(optparse): command line parsing
- library(ordsets): Ordered set manipulation
- library(pairs): Operations on key-value lists
- library(persistency): Provide persistent dynamic predicates
- library(pio): Pure I/O
- library(predicate_options): Declare option-processing of predicates
- library(prolog_pack): A package manager for Prolog
- library(prolog_xref): Cross-reference data collection library
- library(quasi_quotations): Define Quasi Quotation syntax
- library(random): Random numbers
- library(readutil): Reading lines, streams and files
- library(record): Access named fields in a term
- library(registry): Manipulating the Windows registry
- library(simplex): Solve linear programming problems
- library(solution_sequences): Modify solution sequences
- library(tabling): Tabled execution (SLG)
- library(thread_pool): Resource bounded thread management
- library(ugraphs): Unweighted Graphs
- library(url): Analysing and constructing URL
- library(varnumbers): Utilities for numbered terms
- library(yall): Lambda expressions
- The SWI-Prolog library
- Reference manual
- To be done
- - Provide type safety while loading
- Thread safety must now be provided at the user-level. Can we provide generic thread safety? Basically, this means that we must wrap all exported predicates. That might better be done outside this library.
- Transaction management?
- Should assert_<name> only assert if the database does not contain a variant?
This module provides simple persistent storage for one or more dynamic predicates. A database is always associated with a module. A module that wishes to maintain a database must declare the terms that can be placed in the database using the directive persistent/1.
The persistent/1 expands each declaration into four predicates:
As mentioned, a database can only be accessed from within a single module. This limitation is on purpose, forcing the user to provide a proper API for accessing the shared persistent data.
Below is a simple example:
:- module(user_db, [ attach_user_db/1, % +File current_user_role/2, % ?User, ?Role add_user/2, % +User, +Role set_user_role/2 % +User, +Role ]). :- use_module(library(persistency)). :- persistent user_role(name:atom, role:oneof([user,administrator])). attach_user_db(File) :- db_attach(File, ). %% current_user_role(+Name, -Role) is semidet. current_user_role(Name, Role) :- with_mutex(user_db, user_role(Name, Role)). add_user(Name, Role) :- assert_user_role(Name, Role). set_user_role(Name, Role) :- user_role(Name, Role), !. set_user_role(Name, Role) :- with_mutex(user_db, ( retractall_user_role(Name, _), assert_user_role(Name, Role))).
- persistent +Spec
- Declare dynamic database terms. Declarations appear in a directive and
have the following format:
:- persistent <callable>, <callable>, ...
Each specification is a callable term, following the conventions of
library(record), where each argument is of the form
Types are defined by
- True if PI is a predicate that provides access to the persistent database DB.
- db_attach(:File, +Options)
- Use File as persistent database for the calling module. The
calling module must defined persistent/1
to declare the database terms. Defined options:
- One of
close(close journal after write),
flush(default, flush journal after write) or
none(handle as fully buffered stream).
If File is already attached this operation may change the
- True if the context module attached to the persistent database File.
- Detach persistency from the calling module and delete all persistent clauses from the Prolog database. Note that the file is not affected. After this operation another file may be attached, providing it satisfies the same persistency declaration.
- Synchronise database with the associated file. What is one
- Database is reloaded from file if the file was modified since loaded.
reload, but use incremental loading if possible. This allows for two processes to examine the same database file, where one writes the database and the other periodycally calls
db_sync(update)to follow the modified data.
- Database was re-written, deleting all retractall statements. This is the
- GC DB if the number of deleted terms is the given percentage of the total number of terms.
- Database stream was closed
- Remove all registered persistency for the calling module
- No-operation performed
With unbound What, db_sync/1 reloads the database if it was modified on disk, gc it if it is dirty and close it if it is opened.
- Sync all registered databases.