Sounds unsafe, but rather have you thought about using safe and easily serialized matchspecs? 
I’m unsure how well this concept works in elixir but I’ve used them extensively in Erlang: http://erlang.org/doc/apps/erts/match_spec.html
How complex is the matching and what is it matching against? Basically a matchspec is capable of everything that a, say, case or function head matching can do, of structure, content, ‘when’, and exactly ‘what’ to match out too and in what format. They are awesome.
There are also a multitude of converters of function declaration definitions to matchspecs that make it easy too, but a simple web gui would not be too hard.
