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[ #131 ] What is Perl? Permalink

English, Perl, Rant Added less than a year ago and last edited less than a year ago

Larry now uses "Perl" to signify the language proper and "perl" the implementation of it, i.e. the current interpreter.

Perl is a language specification. Languages (well, grammars) should be able to be expressed in BNF or EBNF or other formal notations (if you are a perl expert and have just registered alarm bells, refer to note at bottom of post.) If someone likes Perl, it might be because they like the expressiveness of the syntax. Perl can exist without any interpreter or community or libraries. Perl can exist on paper only.

perl is an application or program that runs (interprets) languages written in Perl. There is one major implementation of perl (pre-Perl 6 that is), but there is nothing stopping you from writing your own version of perl right now (except time and incredible effort, again, please see the note at bottom of post) - although you'd call it something else wouldn't you? If someone says they don't like perl, they might be talking about how the internals of the perl application are filled with deep voodoo - that the C that describes and implements perl is hard to follow and hard to extend. Or they might be complaining about the command-line flags that perl recognises. perl requires Perl to exist. If perl was interpreting a language that was not Perl, then it would not be called perl.

~Perl~ is a term I just made up. It describes the combination of Perl, perl, libraries included with the standard distribution of perl, CPAN, the Perl community, Perl books, perl books, etc. If someone says they don't like "Perl" because of something that annoys them with CPAN or perlmonks or even a library that is distributed with perl, then they are talking about ~Perl~. If CPAN didn't exist, Perl and perl could still exist!

Am I always so careful as to use the correct spelling of Perl or perl? No, I'm sure I've stuffed up a lot, including in this blog, but I've been thinking about the distinction lately so I thought I'd post on it. Perl would be useless without perl. perl would be almost useless without ~Perl~. However, if you removed all that is ~Perl~ except for Perl and perl, people would create a new ~Perl~. New libraries, new distributions, new websites etc would spring up, made possible by having a working perl. It would likely be a slightly different version of ~Perl~ than before, and that's OK.

Similarly you can like Python, hate python but love ~Python~. Actually, it turns out that there are at least three major python implementations: the so called "cpython" (the main python app, from python.org); "Iron Python" (a .NET implementation) and jython (written in Java.)

Recently, so I'm led to believe, the performance of java has improved considerably. I remember when I was at uni I would say that I hated Java because of its poor performance. I was wrong to say that, I should have said I hated java (or javac, etc.) Java is the language, and is not what I was talking about. Incidentally I don't like Java either, because I think it is too verbose and requires too much boilerplate. But that's just my opinion!

Is it ridiculous to make these distinctions? I don't think so. Annoying in polite conversation? Almost certainly. I think it's interesting to think of the difference especially with different versions of Python interpreters/compilers (see above) and Perl 6 interpreters/compilers around the place (Rakudo and Pugs for example.) You could say that you hated Pugs, loved Rakudo, loved Perl6 but were disillusioned with ~Perl6~.

Notes:

1. Do I honesty believe anyone will start using the term "~Perl~"? Of course not, I just had to type it differently for the purpose of my rant! It's even impossible to tell just by listening as to whether someone hates Perl or perl or ~Perl~ - but you might try asking them whether they are talking about the language, the executable or the community. At least that way they will be forced to back up their opinion intelligently.

2. Sometimes I see reference to PERL. PERL is a mythical creature of the past, associated with spaghetti CGI scripts from 1997, or with people who don't program much. I don't really think PERL ever existed, and if it did let's pretend it didn't.

3. Can Perl actually be expressed in BNF? Well no, it can't be expressed in BNF because it is not a context-free grammar. This article will show you some examples of very ambiguous Perl statements, and tell you that only perl can interpret them. By that it means that there is lookahead code and certain resulting decisions in perl that are not obvious when looking at the Perl grammar. perl is in fact the one authoritative source on how these ambiguous, context-based examples should execute. This fact might make you think that Perl and perl are tied more closely together than I have made out, and in reality this is very true. But at the end of the day perl is just a program that implements algorithms, like any other program! Even if these algorithms are not documented well, you could still - given enough time and intelligence - write them down in some kind of pseudocode (or even convert them to another programming language.) The logic in this pseudocode in combination with other formal grammar specifications would describe a Perl on paper. This Perl would then be implementable by any number of perls.

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