Compatibility with perl 5
A few days ago I briefly discussed with Nicholas Clark (current perl 5.8 pumpking) about making perl5 code forward-compatible with perl6. A quick look through the mailing list archives didn't turn up anything obvious, and I don't recall any mechanism being presented in any of the Apocalypses, so ... Perl 6, we are promised, will try to run "legacy" code unchanged. How will it spot such legacy code? Doing this reliably is a hard problem, but we can make it easier. I suggest that people put: use perl5; near the top of their perl programs, scripts and modules. This would be a clear indicator to the perl6 compiler that this is a perl5 program without it having to do any complicated and error-prone heuristics. And it could be implemented really easily in perl5 with no changes to the core at all: package perl5; "i don't do anything yet"; If such a null-op pragma were to go into the next perl 5.8.x release people could start preparing their existing code for perl 6 right now. Which is surely a Good Thing. And of course if the pragma were to also be available to download seperately from the CPAN people still using older 5.x releases could still use it. -- David Cantrell
Re: Compatibility with perl 5
On 2004-04-13 at 13:16:02, David Cantrell wrote: > Perl 6, we are promised, will try to run "legacy" code unchanged. How > will it spot such legacy code? My understanding has been that perl6 will assume a program is Perl 5 unless it sees a Perl 6 keyword such as 'module' or 'class'. -- Mark REED| CNN Internet Technology 1 CNN Center Rm SW0831G | [EMAIL PROTECTED] Atlanta, GA 30348 USA | +1 404 827 4754
Re: Compatibility with perl 5
Mark J. Reed wrote:
On 2004-04-13 at 13:16:02, David Cantrell wrote:
Perl 6, we are promised, will try to run "legacy" code unchanged. How
will it spot such legacy code?
My understanding has been that perl6 will assume a program is Perl 5 unless
it sees a Perl 6 keyword such as 'module' or 'class'.
That could be problematic, because if Perl 6 sees something like:
my %myhash;
%myhash{'foo'} = 'bar';
Is it going to think 'ahah, perl 6' or 'perl 5 with errors'?
That's assuming my understanding of hash subscripting and variable
declarations in Perl 6 is even slightly correct, of course.
Re: Compatibility with perl 5
David Cantrell skribis 2004-04-13 13:16 (+0100): > Perl 6, we are promised, will try to run "legacy" code unchanged. How > will it spot such legacy code? Doing this reliably is a hard problem, > but we can make it easier. I suggest that people put: > use perl5; Why change what already works? use 5; no 6; It could be a special case: not throwing a fatal exception, but instead changing the grammar to a Perl 5 compatible one. Juerd
Re: Compatibility with perl 5
On Tue, Apr 13, 2004 at 02:27:08PM +0200, Juerd wrote: > David Cantrell skribis 2004-04-13 13:16 (+0100): > > Perl 6, we are promised, will try to run "legacy" code unchanged. How > > will it spot such legacy code? Doing this reliably is a hard problem, > > but we can make it easier. I suggest that people put: > > use perl5; > Why change what already works? > use 5; > no 6; But "no VERSION" does not work, at least in 5.8.3: [EMAIL PROTECTED]:~$ cat foo use 5; no 6; print "version 5, not version 6\n"; [EMAIL PROTECTED]:~$ perl foo syntax error at foo line 2, near "no 6;" Execution of foo aborted due to compilation errors. and my discussion with Nicholas didn't lead me to believe that it would work in the upcoming 5.8.4 either. -- David Cantrell | http://www.cantrell.org.uk/david All principles of gravity are negated by fear -- Cartoon Law V
Re: semantic and implementation of pairs
I have confused assignement and initialisation in my previous mail. Because they are two different operations, there is no problem they have different semantics. A6 described both operations. It described pairs as arguments used to initialize parameters and pairs in assignement. -- stef
Re: Compatibility with perl 5
Matthew Walton wrote:
Mark J. Reed wrote:
On 2004-04-13 at 13:16:02, David Cantrell wrote:
Perl 6, we are promised, will try to run "legacy" code unchanged. How
will it spot such legacy code?
My understanding has been that perl6 will assume a program is Perl 5
unless
it sees a Perl 6 keyword such as 'module' or 'class'.
That could be problematic, because if Perl 6 sees something like:
my %myhash;
%myhash{'foo'} = 'bar';
Is it going to think 'ahah, perl 6' or 'perl 5 with errors'?
It's going to think 'ahah', perl 5'. Because it doesn't contain any Perl
6 keyword (such as 'module' or 'class'), as Mark said.
=thom
Reality is that which, when you stop believing it, doesn't go away.
-Philip K. Dick
Re: Compatibility with perl 5
Thomas A. Boyer wrote:
Matthew Walton wrote:
That could be problematic, because if Perl 6 sees something like:
my %myhash;
%myhash{'foo'} = 'bar';
Is it going to think 'ahah, perl 6' or 'perl 5 with errors'?
It's going to think 'ahah', perl 5'. Because it doesn't contain any Perl
6 keyword (such as 'module' or 'class'), as Mark said.
But then trying to process that as Perl 5 will result in an error. This
doesn't seem particularly sane to me. Will we have to say
use 6;
on all Perl 6 programs to avoid this kind of thing?
Forgive me if I'm missing something obvious here.
Re: Compatibility with perl 5
David Cantrell writes: > A few days ago I briefly discussed with Nicholas Clark (current perl 5.8 > pumpking) about making perl5 code forward-compatible with perl6. A > quick look through the mailing list archives didn't turn up anything > obvious, and I don't recall any mechanism being presented in any of the > Apocalypses, so ... Well, there is one, as far as I understand it. Your "use perl5;" is spelled "package". That is, perl will assume Perl 6 unless it sees "package SomethingOrOther;" (since Perl 6 calls them "module"s). So, to force Perl 5 interpretation, use: package main; Luke
Re: Compatibility with perl 5
At 4:07 PM +0100 4/13/04, Matthew Walton wrote:
Thomas A. Boyer wrote:
Matthew Walton wrote:
That could be problematic, because if Perl 6 sees something like:
my %myhash;
%myhash{'foo'} = 'bar';
Is it going to think 'ahah, perl 6' or 'perl 5 with errors'?
It's going to think 'ahah', perl 5'. Because it doesn't contain any
Perl 6 keyword (such as 'module' or 'class'), as Mark said.
But then trying to process that as Perl 5 will result in an error.
This doesn't seem particularly sane to me. Will we have to say
use 6;
on all Perl 6 programs to avoid this kind of thing?
Forgive me if I'm missing something obvious here.
You're not, and there is no guaranteed universal heuristic. Being
explicit, via command line switches or executable names, is the
prudent way to go.
--
Dan
--"it's like this"---
Dan Sugalski even samurai
[EMAIL PROTECTED] have teddy bears and even
teddy bears get drunk
Re: Compatibility with perl 5
Matthew Walton wrote:
Thomas A. Boyer wrote:
Matthew Walton wrote:
That could be problematic, because if Perl 6 sees something like:
my %myhash;
%myhash{'foo'} = 'bar';
It's going to think 'ahah', perl 5'. Because it doesn't contain any
Perl 6 keyword (such as 'module' or 'class'), as Mark said.
But then trying to process that as Perl 5 will result in an error.
This doesn't seem particularly sane to me. Will we have to say
use 6;
on all Perl 6 programs to avoid this kind of thing?
Forgive me if I'm missing something obvious here.
The original question was "how do I label my code as Perl 5?" The
correct answer, according to Apocalypse 1, is to start your source with
"package." If you didn't want to put your code in a package, then start
it with "package main".
The other question was "how do I label my code as Perl 6?" The correct
answer, according to Apocalypse 1, is to start your source with "module"
or "class".
Here is the relevant paragraph from the apocalypse:
I hereby declare that a |package| declaration at the front of a
file unambiguously indicates you are parsing Perl 5 code. If
you want to write a Perl 6 module or class, it'll start with
the keyword |module| or |class|. I don't know yet what the exact
syntax of a module or a class declaration will be, but one
thing I do know is that it'll set the current global namespace
much like a |package| declaration does.
=thom
A lot of people become pessimists from financing optimists.
Re: Compatibility with perl 5
Thomas A. Boyer wrote: The original question was "how do I label my code as Perl 5?" The correct answer, according to Apocalypse 1, is to start your source with "package." If you didn't want to put your code in a package, then start it with "package main". The other question was "how do I label my code as Perl 6?" The correct answer, according to Apocalypse 1, is to start your source with "module" or "class". Here is the relevant paragraph from the apocalypse: I hereby declare that a |package| declaration at the front of a file unambiguously indicates you are parsing Perl 5 code. If you want to write a Perl 6 module or class, it'll start with the keyword |module| or |class|. I don't know yet what the exact syntax of a module or a class declaration will be, but one thing I do know is that it'll set the current global namespace much like a |package| declaration does. Righty-ho then. That's not actually all that bad, I'm used to starting files with 'module' in Haskell (where it's not always compulsory but is a good idea) so I'm sure I can cope with a similar thing in Perl 6. Thanks
Re: Compatibility with perl 5
On Tue, 2004-04-13 at 11:16, Thomas A. Boyer wrote:
> Here is the relevant paragraph from the apocalypse:
> I hereby declare that a |package| declaration at the front of a
> file unambiguously indicates you are parsing Perl 5 code. If
> you want to write a Perl 6 module or class, it'll start with
> the keyword |module| or |class|. I don't know yet what the exact
> syntax of a module or a class declaration will be, but one
> thing I do know is that it'll set the current global namespace
> much like a |package| declaration does.
So, there are many ways that Perl 6 could tell. Here's a pseudo-code
(because I don't fully know what Perl 6 will look like yet) example that
is disambiguated in many ways:
#!/usr/bin/perl6
# Use binary "perl6" which defaults to Perl 6 instead of Perl 5.
# This is easy, costs us nothing and does not affect Perl 5
use 6; # Force Perl 6 mode, no need for "no 6" in Perl 5,
# as Perl 6 can safely read "use 5" as "force Perl 5 mode"
class myprog { # encapsulate my program as a class Java-style
# Might need some kind of property to force mainishness
method main([EMAIL PROTECTED]) {
print "Hello world\n";
}
}
Or, if you prefer Perl 5 style:
#!/usr/bin/perl6
use 6;
class null {} # Just for the keyword
print "Hello world\n";
Or, if you prefer C style:
#!/usr/bin/perl6
use 6;
stdout.print("Hello world\n"); # not sure if the invocant will do it
--
Aaron Sherman <[EMAIL PROTECTED]>
Senior Systems Engineer and Toolsmith
"It's the sound of a satellite saying, 'get me down!'" -Shriekback
Re: Compatibility with perl 5
On Tue, Apr 13, 2004 at 09:16:21AM -0600, Thomas A. Boyer wrote: > The original question was "how do I label my code as Perl 5?" The > correct answer, according to Apocalypse 1, is to start your source with > "package." If you didn't want to put your code in a package, then start > it with "package main". This is something that should be brought to a wider audience cos then you won't get more people like me wandering in and asking silly questions. I shall write something up for perlmonks tomorrow. -- David Cantrell | Official London Perl Mongers Bad Influence
