Set algebra solver for Redis.


Stal receives an array with an s-expression composed of commands and key names and resolves the set operations in Redis.


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Getting started

Install Redis. On most platforms it's as easy as grabbing the sources, running make and then putting the redis-server binary in the PATH.

Once you have it installed, you can execute redis-server and it will run on localhost:6379 by default. Check the redis.conf file that comes with the sources if you want to change some settings.


Stal requires a Redic compatible client. To make things easier, redic is listed as a runtime dependency so the examples in this document will work.

require "stal"

# Connect the client to the default host
redis =

# Use the Redis client to populate some sets"SADD", "foo", "a", "b", "c")"SADD", "bar", "b", "c", "d")"SADD", "baz", "c", "d", "e")"SADD", "qux", "x", "y", "z")

Now we can perform some set operations with Stal:

expr = ["SUNION", "qux", ["SDIFF", ["SINTER", "foo", "bar"], "baz"]]

Stal.solve(redis, expr)
#=> ["b", "x", "y", "z"]

Stal translates the internal calls to SUNION, SDIFF and SINTER into SDIFFSTORE, SINTERSTORE and SUNIONSTORE to perform the underlying operations, and it takes care of generating and deleting any temporary keys.

For more information, refer to the repository of the Stal script.


$ gem install stal