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If I was forced to use only one kind of loop for the rest of my days it would be a

by collin (Scribe)
on Sep 29, 2005 at 13:54 UTC ( #496105=poll: print w/ replies, xml ) Need Help??

vote on If I was forced to use only one kind of loop for the rest of my days it would be a

drag
[bar] 29/6%
while
[bar] 67/14%
for
[bar] 68/14%
do while
[bar] 9/2%
labeled block
[bar] 15/3%
major drag
[bar] 20/4%
foreach
[bar] 47/10%
triple nested labeled goto spaghetti loop
[bar] 34/7%
recursion
[bar] 66/14%
matter of time 'til I killed the bastard who forced me to do it
[bar] 123/26%
478 total votes
Comment on If I was forced to use only one kind of loop for the rest of my days it would be a
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by gri6507 (Deacon) on Sep 29, 2005 at 14:03 UTC
    What about GOTO? You could do just about everything with that!

    Update Sorry, I glanced at the "Nested labeled goto spaghetti loop" option too fast and was confused by its accidental reference to The Church of the Flying Spaghetti Monster.

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by prasadbabu (Prior) on Sep 29, 2005 at 14:18 UTC
    while(1) { print "Rest of my days\n"; }

    Prasad

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by adrianh (Chancellor) on Sep 29, 2005 at 14:39 UTC
    print map { uc "$_ " } qw( i cannot believe you missed out map ), "\n"
      Bah. Map is extremely limited. Now fold on the other hand...
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by theorbtwo (Prior) on Sep 29, 2005 at 14:40 UTC

    Really, the only loop you need is a bare block... but if I'm going to play "build your own loop" games, I use while (1) {...}, so I know there's "interesting" games going on.


    Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by diotalevi (Canon) on Sep 29, 2005 at 17:40 UTC
    Hey! Where's my (loop ...) macro!?
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by ambrus (Abbot) on Sep 29, 2005 at 19:12 UTC

    I certainly wouldn't think it's a drag to use just one kind of loop: it can be kind of elegant. However, the rest of my life is just too long, my opinion on which single loop is elegant varies with time. Also I wouldn't use a single loop just because I'm forced to it: I like TIMTOWTDI languages that don't force me to use a single programmign style.

    Scheme basically has one kind of looping construct: tail recursion. However, it has some advanced special forms built upon tail recursion. It has let which is just a short notation for tail recursion. But the most important looping construct is do which is by itself so powerful that one could program using only it. However, using do comes out really good only if you're doing side-effectless programming, which I don't always like. (There's a do form in common lisp too, which is similar in form but very different deep down. That do <disgust>changes the values of loop variables</disgust>, so it's not side-effect-less, and has nothing to do with tail recursion which Common lisp doesn't have anyway.)

    What I've said above is not entirely true: there's one more way of looping in scheme apart from calls and tail calls: call-with-current-continuation is by itself a universal looping construct. It's however not something I'd use as a single looping construct in my whole life. (Even worse than that would be to use only setjmp/longjmp in C.)

    If my mind is in a low level state, I could live with only conditional gotos.

    If I program C, I'd definitely go with for. (That's what I've voted for.) It's just much more general than while. To tell the truth, just about any looping construct is more general than while. It's also nice that you don't have to look at keywords if you only use if and for as they have different number of argumets. So, I definitely don't like while. (Update: I forgot to mention it, but I did mean using only for seriously: Re: Pattern matching)

    At one time, I thought that the best looping construct was { ...; ... and last; ...; redo }. This is not only my mania, as the while loop in bash, and the \loop ... \repeat macros in Plain TeX work like this.

    At that time, I actually wrote a toy language where the only looping construct was ( COMMANDS; *) which executed COMMANDS repeatedly. You can exit from it with the COND ? RET operator which exited from the innermost pair of parentheses iff COND stands, and make the result of the parenthisized expression be RET.

    I certainly wouldn't choose foreach as the single looping construct, as I've learnt that it wouldn't give me a Turing-complete language. In logician terms, we say that you can build constructive languages from foreach, which is a true subset of the set of recursively enumerable languages.

    Update 2010-10-17: see also the other poll Re: My favorite looping mechanism in Perl is:.

      However, the rest of my life is just too long
      Someone has better statistics of heart problems among their relatives than I have... :-)
      wouldn't choose foreach as the single looping construct, as I've learnt that it wouldn't give me a Turing-complete language.
      A language with 'if' statements, blocks and foreach should be Turing complete? Write a state engine with if conditions -- put inside an infinitely looping foreach. (-: To get that foreach, lazy eval would be a feature, of course. :-)

      To chose goto and learn source filtering to get everything else is cheating, I guess.

        That's it: an infinitely looping foreach isn't a foreach. It's not a foreach in perl. It's not a for-each in standart scheme either, as r5rs clearly says that the arguments to for-each are lists. (In some interpreters, you can give an infinite list to for-each, but that's clearly an extension. Others, like mzscheme, raise an error on an infinite list.) For in sh and foreach in csh won't allow you to loop infinitely (except for the new arithmetic for loop in bash, but that's not a foreach loop, it's rather a c-style for loop).

      If I program C, I'd definitely go with for. (That's what I've voted for.) It's just much more general than while. To tell the truth, just about any looping construct is more general than while.
      Now I'm curious. Could you give an example of a loop you could write with "for" that you couldn't write with "while"?
      #include<stdio.h> int main(int argc, char** argv) { int a = 0; while(a++,a<10) { printf("%d\n",a); } }

        In C, there's no such loop. But that's true to goto and most other constructs as well, you know. It's just that I like the foreach version of the loop more.

        While it's true you can do anything you can do with a for loop with a while loop, I picked for.

        I really like the capability that for gives you to keep all the operations controlling the loop - initialisation, incrementing and testing - in one place. In C99 (and Perl) you can declare variables in the for statement, and they will have a scope of precisely the for loop. You'll need an extra block to do that with while. So taking the example above, I assume this is intended to synthesise (updated:) ambrus noted that this is equivalent to:

        // UNTESTED for(int a = 1; a<10; a++) { printf("%d\n",a); }

        In fact, you'll need an extra block to get the correct scope:

        // UNTESTED // UPDATED: de-obfuscated { int a = 1; while(a<10) { printf("%d\n",a); a++; } }

        Which is starting to look rather messy.

        Context switch back to Perl here!

        Synthesising while and foreach from for seems reasonably intuitive to me on the other hand.

        # UNTESTED for (;EXPR;) BLOCK # leave first and third EXPRs blank to be # equivalent to while (EXPR) BLOCK # UNTESTED for (my @list = LIST, VAR = shift @list; # iterate manually through @list; # LIST in "for" to be VAR = shift @list) BLOCK # somewhat like # foreach VAR (LIST) BLOCK # without the usual aliasing

        OK, the foreach is starting to look a bit funny, but a foreach from while will be worse, and spread into the block, rather than be confined to the statement itself.

        One issue is that for doesn't have a continue block, but as I come from C I don't tend to use those. continue blocks also split up code that happens every time round the loop, which puts me off. for's third expression is roughly equivalent I suppose, but stuffing a large continue block there could hardly be called good style.

        Recursion is another story but I don't think I could live with it as the only looping mechanism. I'd rather have the reverse issue of synthesising recursion, say with a list of hashes, on the rare occasions I really needed it.

        updated in response to ambrus's comments.

        Also, note:

        perl -MO=Deparse -e "for (;<>;){print}" while (defined($_ = <ARGV>)) { print $_; } -e syntax OK

        the for deparses as a while!

      I certainly wouldn't choose foreach as the single looping construct, as I've learnt that it wouldn't give me a Turing-complete language. In logician terms, we say that you can build constructive languages from foreach, which is a true subset of the set of recursively enumerable languages. Who cares about Turing completeness? You're running on a machine with a finite number of states; so a DFA language is all you can really implement in real life. Turing complete languages can't be implemented; just approximated. Godel's theorem implies that any language you design is by definition incomplete; no matter how big you make the field of numbers that it enumerates, you can make an infinite number of infinitely more expressive languages (which is unsurprising, since Cantor proved that there are an infinite number of magnitudes of infinities, making the whole thing hard to talk about...) It's silly to stop with a Turing machine; why not work over a bigger field than the integers, if you're just doing abstract math for the fun of it? And if you're not just doing abstract math for the fun of it, why are you bothering to talk about infinity at all? -- AC
        Who cares about Turing completeness? You're running on a machine with a finite number of states; so a DFA language is all you can really implement in real life. Turing complete languages can't be implemented; just approximated.

        I could attack this statement from the theocretical side. Computer hardware is developping in a very fast pace. Let's imagine you have a system where the state of the program can be saved and reloaded on a machine with more memory, or one that runs on a transparent cluster of machines where new nodes can be added dynamically and old nodes discarded. Such a system could run forever, if you keep updating it with new hardware. While my lifetime or the lifetime of the computer I'm typing on right now is certainly finite, such an advanced system could live forever, if the civilisation doesn't end in some catastrophe. (In fact, Paul Davies argues in his book The Last Three Minutes that a super-entity could do an infinite number of calculations, and discusses this in the two cases of whether the Universe will expand forever and end in a Big Chill, or gravitation will win and the Universe will end in a Big Crunch.)

        However, even if a DFA is all you can implement in the real-world (there are some steps between the DFA and a Turing machine in power of course), I am a mathematician, and I'd like to at least imagine that I have a Turing-complete machine. I use it even if it's only a theocretical construction. I am not an engineer, who uses a ruler to draw straight line, and uses large plastic templates to be able to draw any kind of ellipse. I just draw a bumpy line or a potato by hand, and say it's a straight line (moreover, an infinitely extending straight line that has no width or thickness) or an ellipse. This is a very pleasant, almost god-like state, because I can create objects engineers can't even dream of just by the power of my mind.

        Naturally, this is not the real reason I wouldn't rely on foreach loops. The reason is simply that they're often difficult to use. It's not easy to convert while loops to foreach loops. It's even more difficult to do it if you care about efficency (because I don't just have any DFA, but a DFA with a limited number of states and limited speed of execution). Foreach loops require to use side-effects even if I don't want to, and you could easily avoid it with do loops. Foreach loops come in different versions in each programming language. But the deciding reason is that C doesn't have a foreach loops, so if I decided on foreach, I couldn't use C anymore.

        Update: "it's silly to stop with a Turing-machine" -- you're right with this part. "Why not use a bigger field(?) than the integers" -- indeed, why not: Symbolic calculations with operator overload, Re^3: Illegal Modulus zero.

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by Happy-the-monk (Monsignor) on Sep 29, 2005 at 21:47 UTC

    Lindy Circle
    Lindy Turn.

    Alas, I will now have to write an article to explain what that is...
    (Update: and I keep confusing them, you see.)

    Cheers, Sören

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by gloryhack (Deacon) on Sep 30, 2005 at 00:17 UTC
    while ($bastard -> state() =~ /^alive$/i) { $bastard -> beat(severity => $max); } $cool_looping_constructs -> restore();

      I'm always picky when it comes to using regexes where a simple eq comparison would be fine (but then again, that's just me):

      $bastard->beat(severity => $max) while ( lc($bastard->state()) eq 'alive' ); $cool_looping_constructs->restore();
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by wolfger (Deacon) on Sep 30, 2005 at 01:42 UTC

    Maybe we should abolish all loops entirely, and force programmers to manually iterate.

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by renodino (Curate) on Sep 30, 2005 at 04:25 UTC
      if(($able_to_use eq 'for')||($able_to_use eq 'while')||($able_to_use e +q 'foreach')) { while $living -e or die "Unable to live without a loop $:"; }
      prad
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by ciderpunx (Vicar) on Sep 30, 2005 at 16:16 UTC
    One more kind of loop ...
    $self->try_and_kill_bastard until ($successful);
    ;-P
    Update Just realized you could read that either way. It has been a long week, but I'd like to assure the monks that I'm not feeling suicidal quite yet ...
      unless ($bastard eq 'ciderpunx') { $self->try_and_kill($bastard) until ($successful); }
      Hey, I saved your life ;)

Missing Poll Option!
by Anonymous Monk on Sep 30, 2005 at 23:31 UTC
    Self-triggering event loop! :-)

    You set attribute X which sets attribute Y which sets attribute X which sets attribute Y which sets attribute X ... until the CPU catches fire!

    Hehehehe....

Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by BrowserUk (Pope) on Oct 01, 2005 at 13:38 UTC

    Missing option?

    { ... redo; ... }

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
    "Science is about questioning the status quo. Questioning authority".
    The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by arc_of_descent (Hermit) on Oct 03, 2005 at 03:16 UTC

    Definitely a foreach over a for

    Wouldn't want to be stuck with a $_ in my loops now for the rest of my life. I prefer a meaningful name for the it variable

      (Updated) I rather feel some people would regret their choices. Only recursion can replace all the others, although I voted for for, because recursion is not technically a loop and in many replacement scenarios it would need some horrible overworking to overcome certain scoping issues, but for has enough machinery to replace everything else except recursion. For example, while (condition) is functionally the same as for (;condition;) and do {} while (condition) could be replaced by for (my $first = 1; $first or condition; $first=0) {}
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by theroninwins (Friar) on Oct 04, 2005 at 12:34 UTC
    Well I love while loops ...but that is a personal think :-). They helped me many times before. But here I went for the italian option (shagetthi nested...), since someone would FORCE me to just keep to them. Just to show him what just one sort of loops could mean :-).
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by radiantmatrix (Parson) on Oct 06, 2005 at 21:35 UTC

    What about until? I voted for while, in any case, because I can trivally (if annoyingly) make for loops with while, but the other way 'round is not so easy.

    my $counter = 0; while ($counter <= 5) { print $counter; $counter++; }
    <-radiant.matrix->
    A collection of thoughts and links from the minds of geeks
    The Code that can be seen is not the true Code
    "In any sufficiently large group of people, most are idiots" - Kaa's Law
Re: If I was forced to use only one kind of loop for the rest of my days it would be a
by saskaqueer (Friar) on Oct 08, 2005 at 15:51 UTC

    I missed the 'triple nested labeled goto spaghetti loop' and wound up voting for the simply uninteresting 'labeled block'. My reasoning behind wanting the triple nested goto block is simple enough: if I'm going to be using the construct for the short eternity of my life, I'd better enjoy using it. Just reming yourself that you are going to drive yourself crazy using one looping mechanism, so you'd might as well choose the crazy one.

    # why code this (equiv: print $_, "\n" for 1 .. 10;) for my $i (1 .. 10) { print $i, "\n"; } # when you can code this? -- untested, no perl # on current box; probably doesn't do what # the above snippet does, but it's suppose to my $i = 0; ONE: { $i -= (8 - 2 * 2 - 2 * 4); # $i += 4 goto FOUR; TWO: { print $i; THREE: { print "\n"; 10 == $i ? exit() : goto ONE; FOUR: { $i += 3 * -1; # $i -= 3; goto TWO; } } } }

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