Set algebra solver for Redis
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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.


Meet us on IRC: #lesscode on

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 is a Lua script for Redis that receives a JSON formatted s-expression and resolves the set algebra operations.

# Populate some sets
$ redis-cli SADD A 1 2 3
(integer) 3
$ redis-cli SADD B 2 3 4
(integer) 3
$ redis-cli SADD C 3 4 5
(integer) 3

# Calculate the intersection of A and B
$ redis-cli --eval stal.lua , '["SINTER", "A", "B"]'
1) "2"
2) "3"

More complex expressions are possible:

$ redis-cli --eval stal.lua , '["SDIFF", ["SUNION", "A", "C"], "B"]'
1) "1"
2) "5"

Stal translates the internal calls to SDIFF, SINTER, SUNION, ZINTER and ZUNION into SDIFFSTORE, SINTERSTORE, SUNIONSTORE, ZINTERSTORE and ZUNIONSTORE respectively in order to perform the underlying operations, and it takes care of generating and deleting any temporary keys. Furthermore, the temporary keys are not replicated to the slaves and are not appended to AOF.

All the nested commands in the s-expression will have a temporary key passed as the first argument. That means only commands that can make sense of that feature can be used in nested expressions.

$ redis-cli --eval stal.lua , '["SINTER", ["SADD", "4", "5" "6"], "C"]'
1) "4"
2) "5"

The outermost command can be practically anything, for example:

$ redis-cli --eval stal.lua , '["DBSIZE"]'
(integer) 3
$ redis-cli --eval stal.lua , '["SCARD", ["SUNION", "A", "B", "C"]]'
(integer) 5


Copy the script and use it directly as shown in the examples. You can also use a wrapper in your preferred programming language.


The following wrappers are available:


The tests are written in Lua and can be run as follows:

 $ lua stal_test.lua

Alternatively you can run make. If there's no output, it means all the assertions passed.