A novel data structure and technique from theorem provers, a pattern matching system and classical term rewriting. Mix it with dynamism and the homoiconic metaprogramming system of Julia. Add algebraic composability. Shake well before using. What could go wrong? Composable compiler transforms, numerical code optimizers, interpreters and compilers, computer algebra systems, categorical theorem provers and much more to come. Come experiment with us and the Metatheory.jl package!