This is, admittedly, more of a personal ramble than a technical article. For the past few years, I have become something of a Crystal believer. Looking at recent movements in Ruby from the perspective of a Crystal believer, I sometimes find myself thinking: “That is the area Crystal people have been digging into for years, and Ruby’s real strengths are not really there, are they…?” I have not been able to share this feeling with many people, which has been frustrating. I myself only really understand Ruby and Crystal, so I have not had much confidence in what I have been thinking, and have spent my time in a somewhat vague state. But if I do not write down these feelings, I will no longer be able to refer back to them, so I decided to summon some courage and write this personal essay. The incompleteness I feel in Ruby is that many operations lack reversibility. You can define a variable, but it is difficult to cleanly delete it. There is include for modules, but there is no de-include .…