Minor nitpick to the nitpick, since I dug down in Elixir's compiler before. Elixir spits out a normal Erlang AST, not a Core Erlang AST, which is a bit different. There are a half dozen levels between the Erlang AST and BEAM as well. There's several instances of a talk by Robert Virding about implementing languages on the BEAM where he talks about which advantages different levels of the compiler to hook into.