4 ms·

Is it really going to be safe to use? I don't know Perl that well, but it feels like there's enough language features to make a safe eval harder than writing yo

Is it really going to be safe to use? I don't know Perl that well, but it feels like there's enough language features to make a safe eval harder than writing your own parser for a DSL. That's certainly the case for Python: https://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html https://nedbatchelder.com/blog/201206/eval_really_is_dangero...

shakna 10y ago
Python's eval is crippled, it can't take a full environment. Suppose for a moment that the scope of eval was truly an environment: And you don't supply the resulting environment with anything but the functions you want. Not even the dot operator, let alone magic builtins. Python's eval suddenly becomes much safer. Unfortunately such an eval is harder to implement in Python, because every object carries it's magic methods with it, rather than looking them up elsewhere.
- hyperpape 10y ago
  Interesting. Is there any language you or the sibling have used that does this with eval, and does it find much use?
  - BuuQu9hu 10y ago
    E and Monte have safe eval() as a consequence of being object-based capability-safe languages; there's no way to cause any effect outside eval() worse than an infinite loop. To the second part of your question: as you have undoubtedly noticed, you've never heard of E nor Monte.
    - hyperpape 10y ago
      Funny that you say that. When I sat down at my machine at work, one of the 100 or so chrome tabs I had open was a page about The Vat: http://www.erights.org/elib/concurrency/vat.html http://www.erights.org/elib/concurrency/vat.html.
      - BuuQu9hu 10y ago
        We have vat documentation too: http://monte.readthedocs.io/en/latest/vats.html http://monte.readthedocs.io/en/latest/vats.html
  - shakna 10y ago
    Sure! Most of the time, it just makes it easier to parse and interpret input in a safe manner. * Racket [0], sometimes used when you don't want to use Racket's way of designing DSLs, or if you want to interface to databases simpler. * Scheme [1], used when designing DSLs, interacting with databases. You often see it go hand-in-hand with X-Expressions. * Lua [2] can, but it is rarely used. Note, the link for Lua actually lists a whole host of languages where this can be technically done, but not all are entirely safe. I think it's uncommonality is not because of it's inconvenience or rarity, but rather the mantra of 'eval is evil' in the programming community, even when it doesn't apply. [0] https://docs.racket-lang.org/guide/eval.html https://docs.racket-lang.org/guide/eval.html [1] https://www.gnu.org/software/guile/manual/html_node/Environments.html https://www.gnu.org/software/guile/manual/html_node/Environm... [2] https://rosettacode.org/wiki/Runtime_evaluation/In_an_environment#Lua https://rosettacode.org/wiki/Runtime_evaluation/In_an_enviro...
abecedarius 10y ago
Python wasn't designed from the start with this kind of security concern in mind. It could have been, like http://erights.org/ http://erights.org/. In such languages it's reasonable to say "you can write a user-level drop-in replacement for eval(), and therefore we can make the built-in eval accessible to all code without any extra security-design concerns" (though of course you still need care in implementation).

shakna 10y ago

Python's eval is crippled, it can't take a full environment. Suppose for a moment that the scope of eval was truly an environment: And you don't supply the resulting environment with anything but the functions you want. Not even the dot operator, let alone magic builtins. Python's eval suddenly becomes much safer. Unfortunately such an eval is harder to implement in Python, because every object carries it's magic methods with it, rather than looking them up elsewhere.

hyperpape 10y ago
Interesting. Is there any language you or the sibling have used that does this with eval, and does it find much use?
- BuuQu9hu 10y ago
  E and Monte have safe eval() as a consequence of being object-based capability-safe languages; there's no way to cause any effect outside eval() worse than an infinite loop. To the second part of your question: as you have undoubtedly noticed, you've never heard of E nor Monte.
  - hyperpape 10y ago
    Funny that you say that. When I sat down at my machine at work, one of the 100 or so chrome tabs I had open was a page about The Vat: http://www.erights.org/elib/concurrency/vat.html http://www.erights.org/elib/concurrency/vat.html.
    - BuuQu9hu 10y ago
      We have vat documentation too: http://monte.readthedocs.io/en/latest/vats.html http://monte.readthedocs.io/en/latest/vats.html
- shakna 10y ago
  Sure! Most of the time, it just makes it easier to parse and interpret input in a safe manner. * Racket [0], sometimes used when you don't want to use Racket's way of designing DSLs, or if you want to interface to databases simpler. * Scheme [1], used when designing DSLs, interacting with databases. You often see it go hand-in-hand with X-Expressions. * Lua [2] can, but it is rarely used. Note, the link for Lua actually lists a whole host of languages where this can be technically done, but not all are entirely safe. I think it's uncommonality is not because of it's inconvenience or rarity, but rather the mantra of 'eval is evil' in the programming community, even when it doesn't apply. [0] https://docs.racket-lang.org/guide/eval.html https://docs.racket-lang.org/guide/eval.html [1] https://www.gnu.org/software/guile/manual/html_node/Environments.html https://www.gnu.org/software/guile/manual/html_node/Environm... [2] https://rosettacode.org/wiki/Runtime_evaluation/In_an_environment#Lua https://rosettacode.org/wiki/Runtime_evaluation/In_an_enviro...

abecedarius 10y ago

Python wasn't designed from the start with this kind of security concern in mind. It could have been, like http://erights.org/ http://erights.org/. In such languages it's reasonable to say "you can write a user-level drop-in replacement for eval(), and therefore we can make the built-in eval accessible to all code without any extra security-design concerns" (though of course you still need care in implementation).