Right. Perhaps a better way to summarize this is that:
* Lisp made the first giant step of having code representable as data for meta-programming, and chose sexprs to do so
* Common Lisp came later, and made the important step of requiring this representation, which means that in every CL implementation you're required to have the code as data aspect
* But the flip side of this is that CL hard-wires just sexprs, it forbids an extended type, which means that you can't get anything more than sexprs (without resorting to "extra properties" hash table tricks)
* Meanwhile, Scheme (R5 and others that have only `syntax-rules') took a step back by specifying only rewrite rules which can be implemented in any way an implementation chooses
* But some Scheme implementations did use sexprs, but since they need to encode more information (lexical context) they extended them into syntax values (note that some Scheme low-level macro systems try to present users with a simplified interface where user code sees just the sexprs)
* Later on, Racket took further steps and enriched its syntax values with "more stuff"
* R6RS got closer to this too, by adopting the syntax-case system (but some people had issues with "wrapping" symbols, since you can't do that with the hash table trick)
* And finally, R7RS (the "small" version) is going to take a step back into the R5RS days. (And in the "big" language it looks like they'll adopt one of these systems that try to keep the sexpr illusion.)
* Lisp made the first giant step of having code representable as data for meta-programming, and chose sexprs to do so
* Common Lisp came later, and made the important step of requiring this representation, which means that in every CL implementation you're required to have the code as data aspect
* But the flip side of this is that CL hard-wires just sexprs, it forbids an extended type, which means that you can't get anything more than sexprs (without resorting to "extra properties" hash table tricks)
* Meanwhile, Scheme (R5 and others that have only `syntax-rules') took a step back by specifying only rewrite rules which can be implemented in any way an implementation chooses
* But some Scheme implementations did use sexprs, but since they need to encode more information (lexical context) they extended them into syntax values (note that some Scheme low-level macro systems try to present users with a simplified interface where user code sees just the sexprs)
* Later on, Racket took further steps and enriched its syntax values with "more stuff"
* R6RS got closer to this too, by adopting the syntax-case system (but some people had issues with "wrapping" symbols, since you can't do that with the hash table trick)
* And finally, R7RS (the "small" version) is going to take a step back into the R5RS days. (And in the "big" language it looks like they'll adopt one of these systems that try to keep the sexpr illusion.)