13 Apr 2003 apm   » (Journeyer)

I've been doing a little reading on Perl 6 (the new version of Perl currently being designed) and Parrot, the new virtual machine (VM) for Perl and possibly other languages.

You can read some of Larry Wall's (Perl's inventor) thoughts on Perl 6 in his "Apocalypses" at http://dev.perl.ogr/perl6 (along with some material on Parrot). Larry and the Perl people are a smart bunch. But I wonder if they're too smart. Maybe I'm wrong, but they seem to be making Perl so complex that the vast majority of users won't have a clue what they're talking about. I think C++ suffers from this as well. Brilliant hacks, but often beyond us mere mortals. It's easy for the language designer to say "you can just use what you need". But what happens when you have to read (and understand!) someone else's code, that uses a different "subset" than what you know.

Luckily, I'm not brilliant enough to have this problem with Suneido. Although it's all relative and I guess some people would say I have already fallen into this trap. :-)

One interesting thing about Parrot is that it's register based rather than stack based like most other VM's (e.g. Suneido, Java, Smalltalk). This point was brought up in the Advogato discussion of the Suneido language (http://www.advogato.org/article/209.html) which referenced a paper saying registers are better than stack (http://cm.bell-labs.com/who/rob/hotchips.html). Interestingly, this paper claims reference counting garbage collection is better, whereas Parrot claims the opposite.

Parrot claims it will be general purpose, not limited to running Perl. Maybe a future version of Suneido should use Parrot?

Other interesting points from Perl 6:

  • return, break, continue are "exceptions', similar to how they are implemented in Suneido blocks
  • More "statements" are expressions, e.g. a switch is expression that has a result value. I've been asked why Suneido didn't make all/more statements expressions.
  • Perl 6 is considering .name as shorthand for self.name just as it's shorthand for this.name in Suneido
  • You can put "catch" in any "block" including a function body, "try" isn't required. I like this.
  • do { ... } is an expression that "returns" the result of executing the block
  • Although it was proposed that you shouldn't have to "declare" lexically scoped variables, Larry is against this, saying it's too confusing otherwise. But if, as most people recommend, you keep all functions/methods small, then I don't think this argument holds.

But my biggest lasting impression is that Perl is getting very big and very complex. You can change the compiler's parsing grammar on the fly for gosh sakes. How are you going to understand code where you don't even know the syntax without looking at how the writer modified the language?!

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