When I saw it, I felt the same way (also using Scheme a lot) and I still feel it is messy. However, what I think might be the reason for it, is that it is difficult to store a lambda in Scheme including its whole environment in an object and send that over the wire somewhere else, on a different machine to run. Perhaps distinguishing between Proc, block and lambda gives Ruby a possibility to treat one of them specially, so that it can do these things easily?