Andy Wingo scripsit:
> > "3D" macros allow us to reify "compile-time" values into our source
> > code (think compiled procedures appearing as literal constants in
> > the operator position of a S-expr).
>
> What Scheme implementations actually allow this? Guile used to, but then
> it grew a compiler.
Actually, if you quote the compiled procedure, most Schemes' "eval"
will allow it:
> (define x `(car '(a . b)))
> (set-car! x `(quote ,car))
> (eval x (interaction-environment))
a
I tested Chicken, SCM, Gauche, Gambit, Guile, Bigloo, and Chez
successfully. MIT Scheme doesn't like "interaction-environment",
mzscheme doesn't like "set-car!", and Scheme48/scsh report vm-exceptions
when doing the set-car!.
--
John Cowan [email protected] http://ccil.org/~cowan
"The exception proves the rule." Dimbulbs think: "Your counterexample proves
my theory." Latin students think "'Probat' means 'tests': the exception puts
the rule to the proof." But legal historians know it means "Evidence for an
exception is evidence of the existence of a rule in cases not excepted from."
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