[e-lang] Reentrancy via Recursion

[David-Sarah Hopwood]

Kevin Reid wrote:
> On Feb 26, 2009, at 5:46, Toby Murray wrote:
> 
>> Would the addition of another invocation operator (on top of "." and
>> "<-") to E that means
>> "immediate-call-to-untrusted-object-that-shouldn't-be-able-to- 
>> recursively-call-me" be fair? Being able to use such an operator
>> would enable the programmer not to have to worry about these kinds
>> of bugs.
> 
> Having such an operation would expose (by whether it succeeds or  
> fails) information about the stack, and break determinism.

I don't think it exposes information about the stack that isn't
already available to the user of such an operation. An object O
can simulate this operation (or a similar per-object restriction)
by setting a private flag before making the invocation, and then
checking whether the flag is set whenever O is entered.

Since the simulation is deterministic, so is the proposed operation.

-- 
David-Sarah Hopwood ⚥