On Fri, Aug 02, 2002 at 05:20:45PM +0200, Jerome Vouillon wrote:
> On Thu, Aug 01, 2002 at 10:57:34AM -0700, Sean O'Rourke wrote:
> > My naive implementation would have an array of hashes for each sub, with
> > one entry for each level of scope within.
>
> I would use an array of arrays or a linked-list of arrays. This is
> hardly more difficult to implement (you just need to keep track of the
> variable indices during compilation) and the generated code will be a
> lot more efficient.
Sorry if I've got confused and missed a bit, but if anyone is able to
eval new code in your scope, then you'll also have to keep the mapping of
variable names to array indexes somewhere. Although I agree that numeric
lookup in the generated code ought to be much much faster.
> > Waving my hands somewhat more quickly, as an optimization, lexicals can
> > just live in registers when the compiler sees no references to %MY or
> > closures. Nastiness like eval and caller.MY can be handled by inserting
> > fixup code to reconstruct the lexical array on demand.
>
> caller.MY is especially nasty because you have to pay for it even when
> you don't use it: you can't know whether a function has to support it
> just by looking at the function code. It will be really tricky to
> implement any optimization if one can write things like:
> caller(1).MY{'$y'} := $x
You can't know whether a function has to support it by looking at all the
bytecode in the interpreter at any given time. Some "nasty" programmer only
needs to dynamicly load a library that goes up from its scope into yours and
your careful check is worthless.
Nicholas Clark
