OpenEuphoria

Re: Crash or return forbidden value?

• Posted by Shawn Pringle <shawn.pringle at gmai??com> May 08, 2008
• 642 views

CChris wrote:
> 
> Currently, the interpreter always checks the validity of any index or slice,
> and errors out whenever a test fails.
> 
> My point is: there is no need to duplicate the testing made by the
> interpreter,
> and it should do the testing. Just allow RTFatal() to do something smarter,
> like skipping the call or branching to some place. This would make the user
> code more efficient (no duplicate tests) and cleaner, as part of the error
> handling
> will simply be in the backand, where it is already. 
> 
> CChris

What you are talking about here is building an Exception system into the
interpreter.  It would be analogous to try/throw/catch and Exceptions like
in Java or C++.  Perhaps exceptions could be less invasive than adding C++ 
syntax if say some new builtin routines such as a register_exception_routine
were added.  Routines that are passed to that function would get called
in case of exceptions.  There would have to be a special return mechanism
for these functions.  They could return to the offending routine's caller.

You can put in some kind of side effect like syntax keyword:
onexception (s[6] = 4) {
 ..
}


On the other hand, perhaps compiled code could remove the second check
after an if statement.

s[6] = 5 -- check is done to make sure s is a sequence and 6 is a valid index

if sequence(s) and length(s) > 7 then
      s[6] = 5 -- no check is made to make sure s is a sequence for the
                -- the user did it.  Additionally 7 and 6 are constants
                -- so index checking could be eliminated at compile time
                -- too.
end if

Shawn Pringle