Alchemy.Cogs.set_parser

You're seeing just the macro set_parser, go back to Alchemy.Cogs module for more information.
Link to this macro

set_parser(name, parser)

(macro)

Allows you to register a custom message parser for a command.

The parser will be applied to part of the message not used for command matching.

prefix <> command <> " " <> rest

Examples

Cogs.set_parser(:echo, &List.wrap/1)
Cogs.def echo(rest) do
  Cogs.say(rest)
end