[vidarh]

They're not three different abstractions.

The distinction between a block and a Proc is an implementation detail - an implementation can choose to always make blocks Procs (my experimental Ruby compiler does just that) and a program shouldn't be able to tell the difference.

The distinction between proc and lambda with respect to how returns are handled provides significant utility with very low added implementation complexity that for the most part work together to do what people will expect of them.

That is, the most logical reading of the block syntax is that a return will return from the function it is lexically in, so it does, while a lambda looks like a function, and acts accordingly.

If anything, to me these are prime examples of what makes Ruby a great language that values developer happiness over pointless exercises in purity.