On Wed, Jul 3, 2019 at 7:31 PM Phil Hofer <xxxxxx@sunfi.sh> wrote:

Consequently, a "safe" subset of R7RS must restrict the
implementations of define-syntax, letrec-syntax, etc. to
only accept hygienic syntax transformers.

R7RS-small has no other kind of syntax transformer.  On a syntax-case system, a bare lambda would indeed be dangerous, but at least {er,ir,sc,rsc}-macro-transformer are unavailable.
I also think it might be worth reconsidering the use of the
words "safer" in the title of this SRFI. It's not clear
what "safer" means in this context: what security guarantees
are we actually trying to achieve here?

We guarantee exactly nothing except a lower level of risk than not sandboxing at all.  That's why I was careful to use language like "safer" (as in "safer sex" as opposed to "safe sex", which suggests no risk at all), "less concern", "increased assurance", and "almost certainly".

John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
The internet is a web of tiny tyrannies giving an illusion of anarchy.
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