The characteristics of a DSL are that the source code should look like the original representation of the domain concept. In this case, the domain concept is described by an axiom and a set of rules. Using the algae growth example, it needs to look like the following:

Axiom: A
  Rule: A -> AB
  Rule: B -> A

If we try to write them in plain Julia language, we may end up with code like this:

model = LModel("A")
add_rule!(model, "A", "AB")
add_rule!(model, "B", "A")

As we can see, this is not ideal. While the code is neither long nor difficult to read, it does not look as clean as the L-System grammar. What we really want is to build a DSL that lets us specify the model as follows:

model = @lsys begin
    axiom : A
    rule  : A → AB
    rule  : B → A
end

This will be the target syntax for our DSL.