Hi, I was looking into free monads for designing a DSL for describing scenarios of the form: scenario = do aId <- createA b0Id <- createB id b1Id <- createB id link b0 b1 In our company we use a graph database, and currently we're setting up the test data using raw queries O.O So I wanted to come up with a better abstraction, and also enable us to do property based testing (by testing on random scenarios like the one above). Anyway, I ran into this presentation: http://www.slideshare.net/jdegoes/mtl-versus-free http://degoes.net/articles/modern-fp-part-2 In which monad transformers and free monads are compared. Do you have any experience using any of these approaches. If so would you mind sharing? ;) Thanks! Damian