Teacher: Last week I held a tutorial series with my students on the concept of a functor, with the purpose of taking a fresh look from a few angles they hadn’t considered before.

Lisa: We started gently, but soon built up a heady tower of abstrac­tion, freely wielding the force of functoriality.

Harry: For a newcomer to category theory, I can’t believe how much I learnt. And we were having so much fun, we even continued on into the weekend!

Teacher: Yes, to finish off our week we looked at how we might describe the printf function in terms of monoidal functors.