David Kastrup <d...@gnu.org> writes: > (define (my-eval form env) > (call-with-current-continuation > (lambda (x) > (env (list x form))))) > > (define-macro (my-env) > (call-with-current-continuation > identity)) > > > (format #t "~a" (my-eval '(+ x 3) (let ((x 4)) (my-env)))) > > Mark H Weaver <m...@netris.org> writes: > >> In fact it makes me wonder whether `the-environment' and `local-eval' >> could actually be implemented this way. I see some complications that >> might make this strategy impractical or fragile, most notably that we >> must be assured that the (call/cc) does not happen until >> (the-environment) would have been _evaluated_, whereas the >> expander/memoizer/evaluator will want to see what code is there _before_ >> evaluation. I'll have to think about this. There might be an easy and >> robust way to do this, or maybe not. > > Feel free to experiment with the above. I have my doubt that it leads > to sane behavior. In particular, it will refinish macro expansion (so > you don't want significant material behind it) and reevaluate the > _whole_ eval it is in up to the point of calling my-env (so you don't > want significant material before it). > > So it is more a joke than anything of practical value. But is _is_ good > for a few dropjaws.
Actually, if the evaluator does macro expansion on the fly instead of en bloc, it may even be a practical joke. -- David Kastrup
