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Re^2: Modern Perl 4th Editionby likbez (Acolyte)
|on Nov 19, 2017 at 03:11 UTC||Need Help??|
Instead, I wanted to write a book that explained the design of the language so that people could use it effectively, taking full advantage of the CPAN, and knowing enough that the copious documentation makes sense without needing a couple of semesters of computer science.The road to hell is paved with good intentions.
There is such thing as the "level of abstraction." The ability to operate on various levels of abstraction and switch them at will is the talent closely associated with the software architect talent. If it is absent, the guy is just useless as a software architect and probably is a bad programmer too. You tried to remove all, even existing, links to the lower levels of abstraction (for example, by choosing to cover Moose and avoiding old school "bolted on" Perl OO mechanisms). IMHO that creates the "house of cards" situation. I think that's a dangerous strategy.
My position is that a competent Perl programmer needs to know and strive to learn some C, and should have some genuine interest (at least on the superficial level) on how various Perl constructs are mapped in memory, how Perl interpreter symbol tables are organized and how they are linked to the notion of namespaces, and how garbage collection works. IMHO it is challenging to learn Perl to sufficient depth staying on "pure Perl" level. As a minimum, the person should learn well Perl debugger in addition to the language. From this point of view features that are not well represented in Perl debugger should be avoided. So complete novices, who try to learn Perl "without needing a couple of semesters of computer science," probably should use Minimal Perl book by Tim Maher and stay away from yours.
So I see a problem with a high level "pure Perl" approach, which is what your book is about. There is little coverage of "Perl ecosystem" outside CPAN in your book. Lip service is not enough. There is no chapter about Perl debugger. There is no chapter about Perl ability to call C.
And that's why I think coverage of the "classic" text manipulation functions is important. They represent a lower level of abstraction than regex (and historically they are older than regex; I think substr, index and tr were first defined in PL/1 around 1964; regex history started around 1968.). So coverage of both means adherence to Perl slogan "There's more than one way to do it" and coverage of only one is a betrayal of this slogan. As simple as that.
I think that various levels of abstraction need to coexist in the same language. And that's why I like Perl. But "my Perl" is not the language I have found in your book. Yours is a different Perl.
While the higher level of abstraction represents the progress of the language, that does not obviate the need for the features that exist on the lower level of abstraction. You need to give people a choice, not to corral them into the highest level of abstraction available.
In this sense, the ability to use small C fragments in Perl (see the discussion at XS Library - Embedding C code in Perl), the good understanding of classing string functions as an alternative to regex (Perl, after all, is a great text processing language), etc., are so important and, as such, represent Perl advantages. Classic Perl slogan "There's more than one way to do it" should be interpreted as "There's more than one way to do it on different levels of abstractions." IMHO.
For example, Moose does provide the higher level of abstraction of OO than the "old school" Perl5 "bolted on" OO solution. But the question arises whether the advantages justify the cost and learning curve, as well as how much of it is the pure "syntax sugar" and how much is the "meat." The fact that "Moose is more smooth" does not make it inherently superior. All depends on your needs as a programmer.
The ability to see the OO "Kitchen," even if it is dirty, is also a valuable feature. Especially for students. That's a positive feature of "old school" Perl OO in comparison with Ruby and Python: it does provide access to lower levels of abstraction for OO. People are smart enough to choose what is best for them. But that means that it might be beneficial to cover both in a reference book. I, for example, will not approach Moose, unless I need to maintain somebody else code that uses it.
While creating the higher level of abstraction is the name of the game (and that's why Perl became popular), a "reckless" drive to higher levels of questionable abstractions can be self-defeating. That's what I mean by my "house of cards" analogy.
Many people resent being in the situation when they need to catch a black cat in a dark room (when internals of a complex feature are completely hidden), all those artificial examples of "complexity aficionados" advertising those features in their books notwithstanding. And in such cases, programmers either abandon the language and use a lower level one (for example descending from Python to Java) or just use a more simple subset avoiding 'extra" features with "extra" complexity. That's the reality of the situation as I see it.
That's why when you can't do something via regex or can't figure out how particular feature of Perl regex implementation works or why it works in such a way, programming using index and substr is often the best and quickest alternative solution. The solution that, as I have found, works "well enough" even in cases were regex looks "the thing to use." KISS principle is about being simple, not about the most compact solution of a given problem (although it also has great value, if not taken to extremes).
Your attitude "eliding mention of closures would mean there's no good way to explain grep, sort, or map or even lexical scope" is wrong and IMHO is the attitude of a "complexity junkie." Yes, you can explain closures using map or grep as examples where this notion is potentially useful, but not the other way around. You need to repent ;-)
And please do not try to shoot the messenger. I know that writing a book is a very demanding, and not very rewarding occupation, with unfair criticism being one of the hazards of trade, and I commend you for publishing the "Modern Perl." Please consider my critique as the set of recommendations on how to improve it in future editions.