Macro for using native elixir functions in queries

Wrapping an anonymous function in lambda will cause it to be converted at compile time into standard RethinkDB query syntax. Example:

lambda(fn (x) ->
  x + 5 == x/2
end)

Becomes:

fn (x) ->
  RethinkDB.Query.eq(
    RethinkDB.Query.add(x, 5),
    RethinkDB.Query.divide(x, 2)
  )
end