On Mon, Dec 8, 2008 at 7:20 AM, Jon Zeppieri <[EMAIL PROTECTED]> wrote:
> On Mon, Dec 8, 2008 at 4:01 AM, Yuh-Ruey Chen <[EMAIL PROTECTED]> wrote: > > Breton Slivka wrote: > >> 2) It would be really nice to have a callable value that was > >> garaunteed not to have side effects. > > > > This little comment got lost in the recent deluge of emails, but I too > > would really like some mechanism to avoid or see if a function causes > > side effects (and not just mutability). > > Without a static type system, there's very little you can do. > Sure, you could abandon the proof requirement and turn it into an > assertion, so that if F is annotated as "mutation-free" and if, at > runtime, it tries to perform an assignment, an exception is thrown. > But this doesn't work so well for other computational effects. > Throwing an exception itself is an effect, and it would be pointless > to throw an exception when your code illegally attempts... to throw an > exception. > > Non-termination is an effect, and it's notoriously immune to runtime > checks. > > I/O effects are possibly the most interesting from a practical > perspective, but they're outside the scope of the ES standard. > E's auditors <http://www.erights.org/elang/kernel/auditors/> < http://wiki.erights.org/wiki/Guard-based_auditing> are a mostly non-static approach that can verify many properties, including side effects per se including IO effects, but not including throws and non-termination. Joe-E's similar, but non-extensible and static auditor system < http://www.cs.berkeley.edu/~daw/papers/pure-ccs08.pdf>, has been used to verify some nice purity properties. I am not ready to propose any such thing for Harmony at this time. -- Cheers, --MarkM
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