Message from discussion Is contextual equivalence of a language with quote and eval, like Scheme, trivial or not?
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Subject: Re: Is contextual equivalence of a language with quote and eval, like
Scheme, trivial or not?
From: John Cowan <johnwco...@gmail.com>
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On Sunday, November 11, 2012 9:26:02 AM UTC-5, Pascal Costanza wrote:
> Dynamic binding is not so problematic as you seem to want to make it=20
> appear. It's easy to add dynamic binding to Scheme as a library, and=20
> will apparently be part of R7RS as well. This doesn't affect the rest of=
> the language in negative ways, neither in Scheme, nor in Common Lisp.
It's not whether bindings are dynamic or static (though it happens that in =
Common Lisp all global bindings are dynamic). It's that CL EVAL sees certa=
in bindings of the running program and therefore can affect it in unknown w=
ays. In Scheme this is not true, unless both the program and `eval` are us=
ing the interaction environment. Otherwise, there is a complete firewall b=
etween a Scheme program and anything `eval` can do: in principle, `eval` co=
uld compile and run a program in a completely separate address space, as lo=
ng as it had a copy of the existing dynamic environment.
R7RS support for dynamic binding involves first-class objects; all variable=
s remain lexically bound. Note that R7RS parameters, unlike SRFI ones, are=
n't mutable, so it is transparent whether they are shared or copied by thre=
ads or subprocesses.
Normally I can handle panic attacks on my own; John Cowan <co...@ccil.org=
but panic is, at the moment, a way of life. http://www.ccil.org/~cowan