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All the Perl that's Practical to Extract and Report

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  • Perl's static type system cares more about containers than values. Ponder that for a while, if you really want to confuse the debate.

    • That's actually a point explicitly raised in the article. Dynamic systems focus tracking what kinds of data are used in a system, not on syntactic evaluation of expressions. See the "Problems with Common Definitions" section which begins with this:

      One common saying, quoted often in an attempt to reconcile static and dynamic typing, goes something like this: Statically typed languages assign types to variables, while dynamically typed languages assign types to values. Of course, this doesn't actually defin

      • That's not quite the same. Perl 5's built-in static types are scalar, array, and hash (and Maybe reference, if you pardon the Haskellish pun). You do get compile-time checks on using them appropriately.

        • by btilly (5037) on 2008.07.29 19:12 (#64093) Journal

          While those three are what most people are aware of using, Perl 5 has more static types than that. For example typeglobs. Perl 5 also has a parallel static type system in its attribute system.

          That said, the article did not draw the usual simplistic divisions. And made a point of saying that many languages have both static and dynamic systems, but usually one is more fully developed. Meaning that there are classes of problems that can be solved either through a dynamic type system or a static type system, so once you've solved it one way in a language there is little point in solving it the other way as well.

          This seems to be an accurate description of Perl 5. Perl has both static and dynamic typing. In fact it has at least 2 static type systems, and 2 dynamic type systems! (The second being the taint mechanism.) However the complex things that you'd want from a type system are mostly done with dynamic typing in Perl.

          It will be interesting to see how Perl 6 turns out. My bet is that people will choose to use the dynamic typing heavily, and the static typing features will be more of an afterthought.

          • Inside interface boundaries, quite likely, but I suspect that the use of static types will be quite common for published APIs at least in certain kinds of domains. At the point where client code might lob parameters at you and you can’t be certain that you’ll be called correctly, you need checks on the values anyway, and it’s much easier to do that by declaring signatures than by hand-rolling validation code (or even writing validation profiles for Params::Validate or whatever). Even so I

          • However the complex things that you'd want from a type system are mostly done with dynamic typing in Perl.

            Wouldn't it be more fair to that that the things we think we want from a type system are done with dynamic typing in Perl? Since, as the author points out, you can capture and verify domain specific knowledge via a static type system (see the paper on using static types in Haskell to verify that a database is normalized), it appears that what people are typically doing with static types is rather generic, but their advanced expressiveness (such as catching infinite loops) is not possible with Perl 5, Pytho

            • I didn't say all, I said mostly.

              It is true that an advanced static typing system can do things you simply can't do within Perl 5. On the other hand duck typing allows things that can't be easily done within a static system. Think Test::MockObject and Test::MockObject::Extends.

              However the majority of the day to day utility that most people want from a type system can be delivered either way. It is possible that if more people knew what was possible then our wants could change and that would no longer be t

              • Actually, the paper appears to start with Portuguese for the introduction, but the paper itself is in English. That threw me off, too. Aside from that, your points are well taken.