Redis functions act as a superset of Lua scripts. Instead of sending the script
content with every request (like EVAL), you load the script once as a
"library" and call the functions it registers.
Note
Currently, LUA is the only supported engine.
The library source code must start with the #!lua name=<library_name> shebang.
Inside the script, use redis.register_function to expose your functions.
The registered functions can be called with the FCALL command.