ruby dsl tricks: reifying references

Ruby is great for writing DSLs because it has first class support for two of the most important ingredients of DSLs, contexts and code blocks. With the proper use of instance_eval the same block of code can be evaluated in various contexts to have different kinds of effects but most often what we want to do is evaluate the code block in the “freest” possible context to create an AST (abstract syntax tree). I’m almost certain there is a connection here with initial and terminal algebras in category theory but someone smarter than me will have to chase that analogy. Today I’m just going to demonstrate how to reify references so that we can support cyclic structures in our DSL. Continue reading