I mean originally it was just an exploratory language, something small enough that Steele and crew could keep it all in their head but with lisp flexibility so

I mean originally it was just an exploratory language, something small enough that Steele and crew could keep it all in their head but with lisp flexibility so they didn't have to re-write it everytime they thought up something new. As far as I know it was never meant to be like a tool to teach compiler/interpreter writing or anything. That said a big part of R6 which is mentioned in article is that code was not very portable between R5s (N.B. it wasn't much more portable between R6s) and in some sense if your implementation can't run anyone else's code, what have you actually implemented? Something that looks like scheme is easy implement to be sure but I think R6 was trying to make it so that 'scheme' was a language and not an aesthetic.