Dan Sugalski wrote:
At 4:15 PM +0200 9/23/04, Leopold Toetsch wrote:get_cc(OUT Px) # 1) get current continuation, i.e. the return cont.
In a rare, possibly unique burts of opcode parsimoniousness... perhaps this would be a good thing for the interpinfo op.
That's fine too.
return_cc() # 2) return via current continuation
1) is only needed for special porposes, like passing the continuation on to a different place. The normal way to return from a sub will be 2)
If that's in, access to C<P1> as a return continuation will be deprecated.
Well... should we? We're still passing the return continuation *in* in P1, unless you want to move it out and unconditionally make it a parameter to invoke.
Well, basically, if an interpreter template is used (hanging off the subroutine), the previous interpreter template is the return continuation. That means that for the usual case (function call and return) there isn't any need to construct a return continuation and put it somewhere. The return continuation would only be needed to create a real continuation out of it and pass it along somewhere.
If that calling scheme doesn't fly, its still better to have specific locations in the interpreter context that hold the sub and the return continuation to allow simple function backtrace for the error case or introspection. That's currently not possible, because P0 and P1 can be swapped out into the register backing stack and reused to hold something totally different.
I think I'd also like to make a change to sub invocation, too, to allow passing in alternate return continuations, which makes tail calls easy.
Ok. Good point. We could get rid of C<invoke Px> (call the sub in Px w/o calling conventions) in favor of C<invoke_with_retc Px>. Anyway, the visible part of a return continuation (in above opcode or C<get_cc> would be a continuation. The "normal" case (call/return) could just have that continuation internally in the context. No additional PMC is constructed ifn't needed.
A .returncont arg to the long-form sub call would work fine. If we want to have a variant short-form to support it that'd be fine.
We have that anyway:
.pcc_call sub, retc
leo
