This FAQ is part of the Programmer's Heaven Perl 6 FAQ. It answers questions about moving from Perl 5 to Perl 6.

What is the best way for a Perl 5 programmer to learn Perl 6?

Perhaps one of the best ways is to take small pieces of Perl 5 that you have written and try translating them into Perl 6. That or try solving the kind of problem you would use Perl 5 to solve using Perl 6.

Of course, to get started you will need to read a bit about the new Perl 6 syntax. This FAQ is one good source of information on the changes, and the Perl 6 specification provide much more detailed information.

There are a number of places to turn to for help. One is the Perl 6 forum here at Programmer's Heaven. There is also a perl6-users mailing list; you can subscribe by sending an email to:

perl6-users-subscribe@perl.org

Is Perl 6 backward-compatible with Perl 5?

No. Perl 5 has been a popular and successful language and continues to be as Perl 6 develops. However, there are fundamental issues that need to be addressed in the syntax of the language, and staying backwards-compatible with Perl 5 syntax would have greatly restricted the improvements that were possible. Additionally, the Perl 5 interpreter has grown over the years and become difficult to maintain and add to. Therefore a ground-up design and implementation was required.

There are a lot of things that are good about Perl 5, and a lot of the things that are good about it have been retained. Perl 6 is still very much Perl: it's still great for solving the problems you may have used Perl 5 to solve as well as for other problems that Perl 5 was not so well suited to.

Will I be able to use Perl 5 modules with Perl 6?

Yes; this will likely be achieved by embedding a Perl 5 interpreter, which is what Pugs, one of the prototype Perl 6 compilers, does now. The syntax for using a Perl 5 module is:

use perl5:Module::Name;

The name of a language followed by a single colon is the general syntax for using a module from another language, and in the future, with the Parrot VM, it should be possible to name various languages there.

Will there be a Perl 5 to Perl 6 translator?

Yes, this is currently under development. It uses a modified version of the original Perl 5 parser to build a syntax tree and then takes that and generates Perl 6 code from it.

Does Perl 6 always have "use strict;" turned on, unlike Perl 5?

Not always, just more often. One-liners at the command line, where "-e" is used to specify what to execute, will not have strict turned on. However, it will be on by default everywhere else.

Will Perl 6 programs run faster than Perl 5 programs?

There are way too many factors involved in the performance of a program to give a yes or no answer to this. It is safe to say that it will be possible for Perl 6 programs to run somewhat faster than Perl 5 programs. Some of the improvements are:

• It will be possible to compile Perl 6 down to Parrot bytecode, meaning you save on the parse/compile phase at the start of each run.
• Perl 6 has an optional type annotations system, which means you can give the compiler hints that allow it to generate more optimal code.
• The Parrot interpreter includes a JIT compiler, meaning certain types of code (especially code doing intensive math) may well run notably faster than under Perl 5.
• Multi-threaded programming should be much more resource-efficient than Perl 5 is.

However, be aware that the initial releases of Perl 6 will probably focus on correctness over performance, and that the Perl 6 regex engine will take a while to reach the level of optimization that the Perl 5 one has.

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