> I wouldn't consider something a dialect unless they were similar enough that most code that works in one works in the other with minimal modification. I agre

> I wouldn't consider something a dialect unless they were similar enough that most code that works in one works in the other with minimal modification. I agree, but Scheme passes this test more than you might think. When it originally appeared, it really didn't stand out from the crowd of Lisp 1.5 successors that much at all. It even piggybacked off of its host Maclisp implementation, directly calling Maclisp functions extensively from Scheme, to provide any functionality that there wasn't any point re-implementing (ie, most of it). It was basically just a Maclisp package. Modern Scheme still has a lot of features in common with Maclisp of this time (and by extension Common Lisp), like DO (although Scheme's do has slightly different semantics because it's a macro over tail recursion rather than gotos; subtle differences like this are to be expected between dialects), and it's still based off list structure in exactly the same way that Lisps always have been, so there's still CONS, CAR, CDR, RPLACA (renamed set-car!), RPLACD (renamed set-cdr!), NCONC (renamed append!), and so on. Scheme's lexical scoping also made it back into mainline Lisp, and was a pretty big contribution to Common Lisp. A lot of features like CLOS, SETF, and DEFMACRO (none of which were in Lisp 1.5) are very commonly provided by Scheme implementations. Using the historical argument, there's no question at all that Scheme is Lisp. The majority of ancient Lisp programs can be run under modern Schemes with simple compatibility packages. When all the other Lisps either merged into CL or died, though, Scheme continued to be actively used, and as time went on the Scheme community shared less and less code with the mainline Lisp community. Some people argue that with the modern state of things it's not really useful to talk about Scheme as Lisp now, because they kind of "left" Lisp and went off on their own, philosophically. Scheme definitely began as just another Lisp, though.