foo.erl:
-module(foo).
-export([doit/0, doit/1, doit/2]).
doit() ->
doit.
doit(A) ->
[doit, A].
doit(A, B) ->
[doit, A, B].
Module bar.erl which 'mixes in' foo:
-module(bar).
-include_lib("mixer/include/mixer.hrl").
-mixin([foo]).
or all except specific functions from foo:
-module(bar).
-include_lib("mixer/include/mixer.hrl").
-mixin([{foo, except, [doit/0, doit/2]}]).
or only specific functions from foo:
-module(bar).
-include_lib("mixer/include/mixer.hrl").
-mixin([{foo, [doit/0, doit/2]}]).
Another version of bar.erl which mixes in all functions from foo and select functions from baz:
-module(bar).
-include_lib("mixer/include/mixer.hrl").
-mixin([foo, {baz, [doit/0, doit/1]}]).
One more version of bar.erl which mixes in foo:doit/0 and renames it to do_it_now/0:
-module(bar).
-include_lib("mixer/include/mixer.hrl").
-mixin([{foo, [{doit/0, do_it_now}]}]).
The original motivation for this parse transform was to permit reuse of functions implementing common logic for tasks such as signature verification and authorization across multiple webmachine resources.