Scheme doesn't have data abstraction in the sense Liskov's CLU had it for example, you can try to roll it yourself like SICP does, but it is not the same as hav

Scheme doesn't have data abstraction in the sense Liskov's CLU had it for example, you can try to roll it yourself like SICP does, but it is not the same as having it as a language feature. Also interfaces can still be useful in an untyped language and there has been discussion of their inclusion in Python, see a good discussion here (some of the problems mentioned would apply to Scheme just as well I think): http://www.python.org/dev/peps/pep-0245/ http://www.python.org/dev/peps/pep-0245/ I am not invalidating your observation in general, to the contrary, I just don't agree Liskov is to blame of this here.