Why didn't you conclude instead that first-class (or just multi-shot) continuations are still an experimental feature in Scheme, and that the important part is

Why didn't you conclude instead that first-class (or just multi-shot) continuations are still an experimental feature in Scheme, and that the important part is to warn users of that fact ("use at your own risk, because .. undefined ..")? Have you moved to Common Lisp instead? Edit: I agree that call/cc is pretty nasty; but at least as a debugging (and sometimes hacking) tool it can also be very useful. As a user you can always refrain from using it in regular code. Or decide to use it anyway and suffer from non-portability. So in a sense, the Scheme subset without call/cc is already there, just refrain from using call/cc or any library that uses it? (To be fair, this might be one of the reasons that impedes the growth of portable libraries, but I haven't followed the latest developments of the standardization efforts, and whether things around it are better defined now.) Edit 2: I should also note that there are Scheme implementations that implement activation records more efficiently (in some form that's closer to an array based stack, e.g. segmented stacks or a sort of delayed segmentation approach that Gambit takes), in which case the direct recursive implementation of map that you have shown is more efficient than iteration and then reversal. (And aside of being the straight-forward way to write map, this variant is also easily made into a streaming variant by just adding one |delay| into it (and a |force| for the list argument if |car| and |cdr| don't do that).) One thing I haven't pondered is how call/cc interacts with deforestation like implemented in Haskell, I have to go and experiment with that.