This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2026 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

`redis`

Redis client library. Supports ECLiPSe, GNU Prolog, SICStus Prolog, SWI-Prolog, Trealla Prolog, and XVM.

For general information on Redis, including a list of the available commands, visit:

https://redis.io

API documentation

Open the [../../apis/library_index.html#redis](../../apis/library_index.html#redis) link in a web browser.

Loading

To load this library, load the loader.lgt file:

| ?- logtalk_load(redis(loader)).

Testing

To test this library predicates, load the tester.lgt file:

| ?- logtalk_load(redis(tester)).

The tests assume a localhost Redis server running on the default port (6379) if the REDIS_HOST and REDIS_PORT environment variables are not defined. If the server is not detected, the tests are skipped.

The unit tests were originally written by Sean Charles for his GNU Prolog Redis client library:

https://github.com/emacstheviking/gnuprolog-redisclient

The Logtalk version is a straight-forward port of the original tests using the test/1 dialect of lgtunit.

Supported Redis Features

This library provides wrapper predicates for commonly used Redis operations across multiple data types. For Redis commands not covered by a wrapper, use the generic `redis::send/3` predicate with the command as a compound term.

Connection Management

connect/1 - Connect to localhost on default port (6379)
connect/3 - Connect to specified host and port
disconnect/1 - Disconnect from Redis server
send/3 - Send any Redis command and receive reply

String Operations

get/3 - Get the value of a key
set/4 - Set the value of a key
append/4 - Append a value to a key
getrange/5 - Get substring of string stored at key
setrange/5 - Overwrite part of a string at key starting at offset
strlen/3 - Get the length of the value stored at key
mget/3 - Get values of multiple keys
mset/3 - Set multiple key-value pairs atomically
incr/3 - Increment integer value of key by one
decr/3 - Decrement integer value of key by one
incrby/4 - Increment integer value of key by amount
decrby/4 - Decrement integer value of key by amount

Key Operations

del/3 - Delete a key
exists/3 - Check if a key exists
keys/3 - Find all keys matching a pattern
ttl/3 - Get time to live for a key in seconds
expire/4 - Set a timeout on a key in seconds
persist/3 - Remove the expiration from a key
rename/4 - Rename a key
type/3 - Get the type of value stored at key

Hash Operations

Hashes are maps between string fields and string values, ideal for representing objects.

hset/5 - Set field in a hash
hget/4 - Get value of field in a hash
hgetall/3 - Get all fields and values in a hash
hdel/4 - Delete field from a hash
hexists/4 - Check if field exists in a hash
hkeys/3 - Get all field names in a hash
hvals/3 - Get all values in a hash
hlen/3 - Get number of fields in a hash

List Operations

Redis lists are ordered collections of strings, sorted by insertion order.

lpush/4 - Prepend value to a list
rpush/4 - Append value to a list
lpop/3 - Remove and return first element of list
rpop/3 - Remove and return last element of list
lrange/5 - Get range of elements from list
llen/3 - Get length of list
lrem/5 - Remove elements from list
ltrim/5 - Trim list to specified range

Set Operations

Redis sets are unordered collections of unique strings.

sadd/4 - Add member to a set
srem/4 - Remove member from a set
smembers/3 - Get all members in a set
sismember/4 - Check if value is member of set
scard/3 - Get number of members in a set

Sorted Set Operations

Sorted sets are collections of unique strings (members) ordered by an associated score. Members are unique, but scores may repeat.

zadd/5 - Add member with score to sorted set
zrem/4 - Remove member from sorted set
zrange/5 - Get range of members from sorted set by index
zrank/4 - Get rank (index) of member in sorted set
zcard/3 - Get number of members in sorted set
zscore/4 - Get score of member in sorted set

Usage Examples

% Connect and perform basic string operations
?- redis::connect(Connection),
   redis::set(Connection, mykey, 'Hello World', Status),
   redis::get(Connection, mykey, Value),
   redis::disconnect(Connection).
Status = 'OK',
Value = 'Hello World'.

% Working with hashes
?- redis::connect(Connection),
   redis::hset(Connection, user:1000, name, 'John Doe', _),
   redis::hset(Connection, user:1000, email, 'john@example.com', _),
   redis::hgetall(Connection, user:1000, Fields),
   redis::disconnect(Connection).
Fields = [bulk(name), bulk('John Doe'), bulk(email), bulk('john@example.com')].

% Using lists as queues
?- redis::connect(Connection),
   redis::rpush(Connection, queue, task1, _),
   redis::rpush(Connection, queue, task2, _),
   redis::lpop(Connection, queue, Task),
   redis::disconnect(Connection).
Task = task1.

% Batch operations with mget/mset
?- redis::connect(Connection),
   redis::mset(Connection, [key1, val1, key2, val2], Status),
   redis::mget(Connection, [key1, key2], Values),
   redis::disconnect(Connection).
Status = 'OK',
Values = [bulk(val1), bulk(val2)].

% Key expiration
?- redis::connect(Connection),
   redis::set(Connection, session:xyz, 'user_data', _),
   redis::expire(Connection, session:xyz, 3600, _), % Expire in 1 hour
   redis::ttl(Connection, session:xyz, TTL),
   redis::disconnect(Connection).
TTL = 3600.

% Using send/3 for commands without wrappers
?- redis::connect(Connection),
   redis::send(Connection, info(server), Reply),
   redis::disconnect(Connection).

Credits

This library is inspired by the Sean Charles GNU Prolog Redis client library.

Known issues

Recent versions of macOS seem to disable the mapping of localhost to 127.0.0.1. This issue may prevent running this library unit tests and the `redis::connect/1` predicate from working. This can be fixed either by editing the `/etc/hosts` file or by using in alternative the predicate `redis::connect/3 with '127.0.0.1'` as the first argument.