SWI-Prolog redis client

This package provides library(redis), a client for the redis "open source (BSD licensed), in-memory data structure store, used as a database, cache and message broker".

This is a first version based on the GNU-Prolog pure Prolog redis client by Sean Charles. The main difference to the original client are:

• Replies are not wrapped by type in a compound term.
• String replies use the SWI-Prolog string type.
• Values can be specified as Value as prolog, after which they are returns as a (copy of) Value. This prefixes the value using "\u0000T\u0000".
• Strings are in UTF-8 encoding and support full Unicode.
• Using redis_server/3, actual connections are established lazily and when a connection is lost it is automatically restarted.
• This library allows for using the Redis publish/subscribe interface. Messages are propagated using broadcast/1.

Aim

Redis provides a high performance, low latency store for various shared data structures as well as simple message brokering. In addition it can operate in a cluster, offering high availability. Together with being freely available and extremely simple to setup, this makes redis an ideal tool to share data between multiple servers or establish data sharing between micro services.

Example

This example communicates with the default redis server at localhost:6379. Use redis_server/3 to change the address of the default server or setup a secondary named server.

?- redis(default, set(a, 1)).
?- redis(default, get(a), X).
X = 1.
?- redis(default, set(a, 1 as prolog)).
?- redis(default, get(a), X).
X = 1.
?- redis(default, set(a, hello(world) as prolog)).
?- redis(default, get(a), X).
X = hello(world).

The command mapping is the same as for the original GNU Prolog client. A redis command

COMMAND Arg1 Arg2, ...

maps to the Prolog term

command(Arg1, Arg2, ...)

On return, the mapping depends on the ... as Type annotation. The default is auto, mapping Redis numerical strings to numbers and anything else to an atom:

Redis	Prolog
String	String
Int	Int
List	List
nil	nil (fail if reply is only nil)
Status	status(String)
Error	throws error(resis_error(String),_)

Status

This library is still work in progress. We think the basic interface, using redis_server/3 to register services by name and the predicates redis/1-3 are fine.

• Currently the library is thread-safe using a lock around redis/3. Future versions may use a connection pool that allows multiple threads to make progress.