This Week in Perl 6 (27 May - 2 June 2001)
3 June 2001
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It was a quiet week, with a mere 92 messages across 3 of the mailing lists. There were 9 threads, with 27 authors contributing. 3 threads generated 71 of the messages.
Perl Virtual Registers (continued)
Dan Suglaski summed up his thoughts on the previous week’s register discussion.
1) The paired register thing’s silly. Forget I mentioned it.
2) The interpreter will have some int, float, and string registers. Some stuff will be faster because of it, and it’ll make the generated TIL or C code (when we do a TILperl or perl2c version) faster since we won’t need to call opcode functions to add 3 and 4 together…
3) Whether the registers are really stack-based or not’s an implementation detail. They’ll be based off of some per-interpreter thing, of course, so’ll be thread-local
4) We will have some sort of register push/pop system independent of the register implementation. (Probably, like the 68K family, with the ability to move multiple registers in one go)
5) The bytecode should be really, really close to the final executable form. I’d really like to be able to read in the bytecode in one big chunk and start executing it without change. (We’ll end up with some sections that’ll need to be changed–that’s inevitable. If we can mmap in the non-fixup section pieces, though, that’d be great)
6) We may formally split the registers used to pass parameters from the working registers. I’m not sure if that’ll ultimately be a win or not. (I can forsee lots of pointless register->register moving, and I’m not keen on pointless anything)
This spawned various discussions on several issues:
- 8-bit versus 16-bit opcodes, with 8-bit opcodes having an escape opcode to access extended opcode features. The 8-bit with escapes scheme appears to be the winner.
- CISC-style (high-level) versus RISC-style (low-level) opcodes. Various tradeoffs were discussed, including byte-bloat, processing speed, and ease of translation to other backends. No consensus has been reached yet.
- Pure register versus register/stack hybrid. (In reality, even the pure register scheme is a register/stack hybrid - the question is how much stack play should be involved.) No real consensus on this one, either.
- Variable argument opcodes and how to handle them. It wasn’t expected that any opcodes should not know how many args it was getting passed, but if the situation ever arose, Dan suggested the varargness be buried a layer deeper, and the opcode itself can simply take a single argument - that of the register containing a list of arguments.
Coding Conventions Revisited
Dave Mitchell posted his revised draft of the “Conventions and Guidelines for Perl Source Code” PDD. The revision was generally accepted (save a brief foray into some standard (but relatively tame) tabs and spaces and brace alignment discussions), and the official PDD Proposal should be forthcoming shortly.
It Is Another Language Feature, It Is, Or Is It?
David L. Nicol mused about a new magical variable
it that automatically refers to the last lexically used variable (or perhaps the last variable used as the target of
exists). Most folks found it (in both senses of the word) too troublesome and ambiguous.
Status of the Perl 6 Mailing Lists
There have been, to date, 28 different mailing lists associated with the Perl 6 development effort - a list that seems most daunting at first. That list has now been reduced to eight “open” lists that are currently in use. (The previous lists may be reopened at a later date, and new ones may be created. Annoucements will be made in the usual fashion on
perl6-announce.) Subscription instructions and links to the archives can be found here.
The currently active lists dedicated to Perl 6 are
The last list,
perl-qa, is involved in quality assurance for Perl in general, so it is also included as a Perl 6 development list.
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