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Traditionally computer languages try to be as orthogonal as possible, meaning their features are all at right angles to each other, metaphorically speaking. The problem with that is that people don't solve problems that way. If I'm in one corner of a park and the restrooms are in the opposite corner of the park, I don't walk due east and then due north. I go northeast -- unless there's a pond in the way or something.

-- Larry Wall in interview with Erik Davis, 1998

The clichéd example is, of course, the well-known exercise of getting a language to print "Hello World". In Java, that's:
      class HelloWorldApp {
         public static void main(String[] args) {
            System.out.println("Hello World!");
         }
      }
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It's a cheap shot to point out how syntactically overburdened that is, but it does illustrate a far more important point: that it's *cognitively* over-burdened too ... Perl gets by with:
print "Hello World\n";
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in which the only arcane part is that C-ish "\n" newline. And in Perl 6, even that won't be needed:
say "Hello World";
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And that's what attracts me to Perl. The demands of the language itself don't get in the way of *using* the language.

-- Damian Conway in Builder AU interview

I think the one that has the best broad coverage is Java, but I'm a really biased sample. If you're doing things that are heavily into string pattern-matching, Perl can be pretty nice. I guess actually those are the ones I use much at all these days.

-- James Gosling in Interview with Dennis Ritchie, Bjarne Stroustrup, and James Gosling

Guided by a core set of principles and goals, every language designer is tormented by thousands of agonizing choices. Gosling chose differently to Wall. A perhaps unintended side effect of some of Larry's choices -- such as Perl's "diagonal-ness" and TMTOWTDI -- is that playing golf in Perl is fun. By contrast, and I've never tried it, I imagine playing golf in Java (or Cobol) would feel oppressive in the extreme.

Of course, like obfuscation and poetry, only a minority of Perl programmers actually pursue golf as a hobby. James Gosling, for instance, though he readily acknowledges writing many Perl programs, has never entered a Perl golf tournament, to the best of my knowledge.

This, the fourth episode of the long running series on the lighter side of Perl culture, focuses on Perl Golf.

History

There were secrets to those IBM machines that had been painstakingly learned by some of the older people at MIT with access to the 704 and friends among the Priesthood. Amazingly, a few of these programmers, grad students working with McCarthy, had even written a program that utilized one of the rows of tiny lights: the lights would be lit in such an order that it looked like a little ball was being passed from right to left: if an operator hit a switch at just the right time, the motion of the lights could be reversed--Computer Ping-Pong! This obviously was the kind of thing that you'd show off to impress your peers, who would then take a look at the actual program you had written and see how it was done.

To top the program, someone else might try to do the same thing with fewer instructions--a worthy endeavor, since there was so little room in the small "memory" of the computers of those days that not many instructions could fit into them. John McCarthy had once noticed how his graduate students who loitered around the 704 would work over their computer programs to get the most out of the fewest instructions, and get the program compressed so that fewer cards would need to be fed to the machine. Shaving off an instruction or two was almost an obsession with them. McCarthy compared these students to ski bums. They got the same kind of primal thrill from "maximizing code" as fanatic skiers got from swooshing frantically down a hill. So the practice of taking a computer program and trying to cut off instructions without affecting the outcome came to be called "program bumming," and you would often hear people mumbling things like "Maybe I can bum a few instructions out and get the octal correction card loader down to three cards instead of four."

-- John McCarthy's grad students playing golf ("program bumming") in machine language on the IBM 704 computer in 1959 (from Hackers, Heroes of the Computer Revolution by Steven Levy)

I recently read an article where Knuth describes a game of golf on a 50's machine. The machine read cards, and one could put 8 machine instructions on a card. The goal was to write a program fitting on one card that would read in a number, and reverse it. Noone was able to do it, but Knuth once stunned his fellow students. He came in, put a card in the reader, entered the number 123456789, ran the program, and the program outputted 987654321. Of course, the program would always output 987654321, regardless of the number on input. Later, the machine got an extension. A whopping extra register, with front panel toggles. Which could be used to store an instruction as well. Knuth was delighted that that enabled him to write a single card program that reversed a number.

-- Abigail talks about Knuth on comp.lang.perl.misc 23 March 2001

The competent programmer is fully aware of the strictly limited size of his own skull; therefore he approaches the programming task in full humility, and among other things he avoids clever tricks like the plague. In the case of a well-known conversational programming language I have been told from various sides that as soon as a programming community is equipped with a terminal for it, a specific phenomenon occurs that even has a well-established name: it is called "the one-liners." It takes one of two different forms: one programmer places a one-line program on the desk of another and either he proudly tells what it does and adds the question, "Can you code this in less symbols?"---as if this were of any conceptual relevance!---or he just says, "Guess what it does!". From this observation we must conclude that this language as a tool is an open invitation for clever tricks; and while exactly this may be the explanation for some of its appeal, viz., to those who like to show how clever they are, I am sorry, but I must regard this as one of the most damning things that can be said about a programming language.

-- Edsger Wybe Dijkstra (1930-2002) in his 1972 essay: The Humble Programmer (cited in On Golf)

As indicated by the quotes above, playing golf in computer languages started long before Perl did. It's just that it wasn't called golf back then.

Perl's main claim to fame in this golf business is that a Perl hacker, namely Greg Bacon, actually coined the term Perl Golf in a comp.lang.perl.misc thread on 28 May 1999. And the term golf has been applied to other computer languages since then. Ironically, Greg may have intended the term as derogatory -- just as Fred Hoyle coined the term "Big Bang" to mock that theory -- because Greg once dismissed golf as really, really boring.

As you might expect, the earliest exponents of Perl Golf were probably Larry and Randal. For example, here is an early golfish Larry post from March 1990. And in this one Larry implies that Randal was his golfing buddy in those early days.

In March 1995, Adam Back and Hal Finney caused a stir by implementing RSA encryption and decryption in Perl as a signature file. Later Clifford Adams and others joined in the fun.

In September 1995, in what was probably the first golf contest with money prizes, the surprising winner of this comp.programming.contests C golf contest was a Perl hacker (some might say the Perl hacker;-). The goal of this competition was to find the shortest C program that reverses all words in a file. I found this exchange amusing.

: >Well, if that's your goal, you're gonna have to work a little harde
+r.
: >I sent this out last week, but it never made it off my machine.  It
+'s
: >50 characters, counting the final newline.
: >
: >    main(){system("perl -pe 's/\\w+/reverse$&/eg'");}
: >
: >It's almost readable, too.
: >
: >Larry Wall
:
: Well, if we're allowed to write our own interpreters then yours is
: easy to beat!
:
:     main(){system("a");}
:
: 20 characters! (Not counting the final newline.)
:
: You haven't heard of my interpreter "a"?  Well it just so happens
: that, without any command line arguments, it filters stdin to stdout
: in a manner that is identical to any of the valid entries to this
: competition, like your entry above for example.  :-)
:
: John Ellson

Well, hey, I said you'd have to work a *little* harder, not a lot hard
+er.  :-)

Larry
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Jumping forward to July 2000, Uri Guttman initiated the ill-fated Perl Golf Apocalypse scheduled to run, accompanied by witty commentary, in front of a live audience at TPC 4. Alas, a number of technical glitches caused the event to be cancelled, replaced by a Damian Conway talk. Given that Larry was in the audience, it's little wonder that Uri is still scarred by it today. To my knowledge, no one has been brave enough to attempt a live Perl Golf contest since. The Apocalypse questions formed part of a golf competition run by jmcnamara in PGA Golf, Round 1 and PGA Golf, Round 1 - Results here at the monastery. I note with interest that mtve found some improvements to the original contest solutions some years later (this seems to be a speciality of mtve and thospel).

During 2001, there was such a rush of golf posts here at the monastery, that chipmunk sent out a plea, Tips on Writing a Golf Challenge, to calm things down a bit.

Just before Christmas 2001, the fwp mailing list exploded with a flurry of golf threads, starting with the Santa Claus Golf Apocalypse won by Eugene van der Pijll. This tournament introduced an innovation: strict rules and a test program that all entries must pass before being accepted. A much improved version of this early test program can be found here. These golf contests spawned a new mailing list golf@perl.org, split off from fwp.

A new magazine, The Perl Review, launched early in 2002, sponsored a series of golf tournaments run at SourceForge by Dave Hoover and Jérôme Quelin. These tournaments were run monthly throughout 2002, the top five money winners at the end of season being:

1  Ton Hospel                 $ 4,384,000.00 (10/13)
2  Rick Klement               $ 3,712,000.00 (12/13)
3  Eugene van der Pijll       $ 3,540,000.00 (10/13)
4  Stephen Turner             $ 1,955,200.00 (11/13)
5  Mtv Europe                 $ 1,837,040.00 (9/13)
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In 2003, the TPR tournaments moved to Terje Kristensen's minigolf site where Ton Hospel, Mtv Europe and Rick "tybalt89" Klement continued to dominate. Around this time, golf enjoyed a surge of popularity in Poland, courtesy of games run at the kernelpanic.pl web site and the Polish comp.lang.perl newsgroup. After two to three seasons, these sites became inactive and the game of Perl Golf transmogrified into Code Golf. Serious golf competitions in Perl, Python, Ruby and PHP are nowadays run at Code Golf, while less serious ones (in 51 different languages) are played at shinh's golf site.

What is Perl Golf?

Is it an art, a sport, just a bit of fun, a waste of time, or a threat to sound coding practices? I don't want to dwell too much on this; it is different things to different people. Hopefully, as with obfuscation, people are sensible enough to not start golfing on production code. My personal view is that golf is mostly about fun and competition.

As for the usefulness of Perl golf, apart from being a fun way to explore TMTOWTDI, notice that Perl golf, by its nature, pushes the language to its limits, often exercising boundary conditions. It should come as no surprise therefore that quite a few perl bugs have been unearthed during golf tournaments, especially by Ton Hospel.

Golf Competitions

I think Felix (the contest judge) made a bad judgement, because the winning program was not nearly as confusing as mine---it was actually very simple.

-- MJD on TPJ OPC 5 judging at perl.plover.com

Competitions requiring judges, such as Olympic gymnastics and obfuscated Perl competitions, are easily spoiled by poor judging, as alluded to above by MJD. The wonderful thing about Perl Golf competitions compared to obfuscated ones is that golf is typically judged simply by counting up the number of characters in your solution. I've never seen any ugly disputes or complaints about who should have won.

Of course, the winning golf solution may be horribly ugly or highly inefficient. So several people have suggested alternative types of competitions, judged by different criteria. Perhaps the most commonly suggested is the 100 metre dash where each solution is timed and the fastest wins. A novel twist on this idea is to measure not the CPU or wall clock time, but the number of Perl ops. For more information on Perl ops see Nicholas Clark's excellent paper "when perl is not quite fast enough". Yet another alternative is MJD's Perl Quiz of the Week where human judges comment on the "quality" of a solution after a 60 hour grace period.

The story goes that Marshall discovered this variation 9 years before he played it, and avoided defending with the Ruy Lopez for 9 years until he had a chance to spring it on Capablanca.

-- Quote taken from note by Bill Wall (any relation to Larry?)

It's a mark of Capablanca's genius that he was able to refute over the board a variation his grandmaster opponent had been studying and preparing for nine years.

In similar style to Capablanca, during the TPR tournaments four expert golfers would sometimes cook up a problem, study it in consultation for a month, and conclude the best solution possible was, say, 120 strokes. Yet within a couple of hours, the remarkable Ton Hospel would then go and post a score of around 100!

In many ways, Perl Golf tournaments resemble a fiercely contested chess tournament.

Some Classic Golf Games

One golf that seems to come up again and again is the famous 99 bottles of beer song. It's been discussed here at the monastery in: 99 bottles, 2 lines, 99 Bottles Of Beer (can't we do better), 99 bottles of beer on the Wall, Golf: Back to those damn beer bottles again... and Bottle Golf. For the record, I believe the shortest known solution is not in any of those nodes, but was concocted by thospel and mtve as follows:

sub
b{[@b=(abs||No,bottle."s"x!!++$_,of,beer),on,the,wall]}print
"@{+b},\n@b,\nTake one down, pass it around,\n@{+b}.\n"
for-pop||-99..-1
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This version takes a command line argument specifying the number of bottles (default 99). If you find a shorter one, respond away! May 2011 Update: Shorter bottle golf solutions are now described in Drunk on golf: 99 Bottles of Beer.

The most interesting golf games occur when several solutions, all with a similar score, are possible. To illustrate, consider TPR(0,5a), an infix to postfix converter. This problem could be solved with: an operator stack; via overload; a recursive regex; top-down parsing; or Eugene's winning Mad Dutch algorithm (invented for this game). Sometimes, a truly astonishing approach is found, as when Jukka Suomela in TPR(0,4b) observed that perl itself has a built-in topological sorter: the garbage collector. Chris Dolan's explanation can be found here.

Some Standard Golfing Techniques

Common operations should be "Huffman coded." That is, frequently used operators should be shorter than infrequently used ones.

-- Larry Wall in Apocalypse 3
: OK.  Still, it'd be nice to get anonymous scalars somehow.

The Huffman encoding of that is do{\my$x}.
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-- Larry Wall on p5p, 30 April 1999

An excellent introduction to the basics of shortening your Perl code be found in Perl Golf 101.

As discussed in this thread (update: and this thread and here), some well-known golfing techniques are:

Golfing Technique                     Inventor           Year
-----------------                     --------           ----
@{[]}  aka baby cart                  The Larry or       1994
                                      The Schwartz
}{     aka eskimo greeting            The Abigail        late 1990s
~~     aka inchworm                   ???
~-     aka inchworm-on-a-stick        The Hospel         2002
$_ x= boolean expression              The Larry          early 1990s
y///c aka Abigail's Length Horror     The Hall           1996
stuff value into $\ for printing      The van der Pijll  2001
}for(...){ variation of eskimo        The Hospel         2001
--$| magical flip-flop                The Hospel         2002
\$h{X} is one less than ++$h{X}
       aka Thelen's Device            The Thelen         2002
-i and $^I for data value             The Sperling       2002
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References

Other Articles in This Series

Updated aug 2011: Added John McCarthy (1959) and RSA (1995) reference.

In reply to The Lighter Side of Perl Culture (Part IV): Golf by eyepopslikeamosquito

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