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in loops, these alias may be useful, by cutting down in code clutter. It also has the advantage of still being instantly identifiable in its purpose.
=========================
break if(statement); ---- breaks current loop if statement is true
} if break { ---- performs statement if the loop
didn't end organically
========================
Example usage of above alias to break infinite loop:
------------------------------
int ever = TRUE;
for ( ever ){
__break if ( ever );
__alert( 'forever more!');
} if break {
__alert( 'loop ended prematurely' );
}
=======
Best usage for "break if", is possibly during recursive loops
======
edit: Perhaps we could also have "if break(flag)" or "if break[flag]", and "break(flag) if", if we have different breaking states.
e.g.
int number = 3;
for ( TRUE){
__break(1) if ( number == 1);
__break(2) if ( number == 2);
__break(3) if ( number == 3);
} if break(1) {
} if break(2) {
} if break(3) {
__alert("This alert has activated!");
}
---
EQUIV TO
---
int number = 3;
int flag = null;
for ( TRUE){
if ( number == 1){flag=1;break;}
if ( number == 2){flag=2;break;}
if ( number == 3){flag=3;break;}
}
if ( flag == 1 ) {}
if ( flag == 2 ) {}
if ( flag == 3 ){alert("This alert has activated!");}
COMEFROM Statement
http://www.fortran.com/come_from.html
An alternative program-flow statement for your consideration. [zen_tom, Feb 20 2012]
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Description (displayed with the short name and URL.)
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I've only programmed in a few languages, but I think
things like this already exist, no? |
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especially the "if break" statement, which would be a specialized alternative to "else if" statement |
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am hoping to see it used in python, as I can imagine this would be great use to keep code easy for newcomers to understand. |
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have you considered the "google" statement ? |
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Logically this is very similar to while() or repeat... until() statements. The idea of multiple breaks is dealt with by having ORs in the while() or until() condition. |
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yes but python *has* a 'break' keyword... coincidentally, at first glance anyways, it looks like it does exactly what [am] wants. |
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---FlyingToaster, Feb 15 2012 |
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I have googled it, and yes I know that generally the syntax tends to go like this |
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All I'm asking is to also have |
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instead, as it is more intuitive. I don't think any programming language does that. Well not that I found in google at least. |
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Also for "} break if {" , it saves you from having to use 'flags' to identify if it fully looped or not. |
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Yes it does seem not needed. I shall remove that usage example. |
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seems pretty reasonable to me. The break cases don't exist
but could be implemented by wrapping the call into a
seperate function: |
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OTOH: isn't that exactly what exceptions do? |
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if(condition1) throw Exception1; |
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if(condition2) throw Exception2; |
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In C you can make a macro for "break if": |
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#define break_if (blah) if(blah){break;} |
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You've given two examples: |
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the second, with the exception of the redundant logic, is easily handled by a "goto depending on", "alter"<insert big newbie warning here>, or a "case" type statement. |
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For the first, I can sortof see it if you're defining a very unusual exception condition. The machine doesn't care but using bass-ackwards syntax might make it easier for a programmer to parse a program-dependent logical exception. |
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But that's what comments are for. |
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"break if..." already exists in Ruby. It's just a case of the
generalized form "<statement> if..." For example:
10.times do |x|
print x if x % 2 == 0
break if x == 5
end
Output: 024
The "if break" functionality doesn't exist per se, but since
you can
have a block return a specified value with the break
statement,
you can effectively emulate it (with more functionality)
as
follows:
case 10.times do |x|
print x if x % 2 == 0
break :error if x == 5
end
when :error
puts "ERROR"
end
Output: 024ERROR
So, in conclusion, you should just use Ruby, because
everyone
should use Ruby. |
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Can't argue against that logic. Wonder why the
slower uptake of ruby compared to python. The ruby
code does look a touch more cryptic than python. |
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As for "<statement> if...", this looks like something
python should do. |
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I think the slower uptake is due to several factors, not the least of which is considerable head-
start Python had over Ruby. Python was originally released four years prior to Ruby, and Ruby
wasn't very well known outside of Japan for several years after its initial release. And since a
significant part of both the Python and Ruby user base consists of Perl refugees, a lot of those
people just ended up going to Python and staying there once they got sick of dealing with Perl,
because it was essentially the only other game in town at the time. So only the ones (such as
myself) who never really got along with Python ended up gravitating to Ruby once it became a
viable option. |
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There also don't seem to be too many Python to Ruby converts. Ruby is an unbelievably flexible
language, and I think that flexibility tends to put Python users off. Since everything in Ruby is an
object, and every object can be modified more or less without restrictions, you can change or
extend the entire language in pretty much any conceivable way. I guess you either appreciate
and embrace that flexibility, or you fear it; in my experience, Python users tend to fear it. I'm
not sure why, because while it might seem to make Ruby code a nightmare to follow and
maintain, in actual practice Ruby tends to produce some of the most easily readable and
maintainable code I've ever seen. I don't even bother commenting my code most of the time,
because I rarely have trouble understanding programs I've written months or years ago. This
stands in stark contrast to Perl, where even provided liberal comments throughout, my eyes
would immediately glaze over upon reading the source to a program I'd written two weeks
earlier. |
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In the end, I think it comes down largely to inertia. Admittedly, I have only limited experience
with Python (although I've had to use it on occasion as it's the embedded scripting language in a
few applications I use), but I really don't see why anyone who really puts in the effort to give
Ruby an honest try would want to go back to Python. But since Python is a perfectly serviceable
language (especially compared to Perl), I imagine most Python users don't feel much of a need to
look into anything else. It's too bad, because they have no idea what they're missing (come to
think of it, I feel the same way about Windows users too!) |
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I'm no expert and i only know prehistoric
programming languages, but don't things like
TIMEOUT, EXIT and LEAVE do this sort of thing? |
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If you're trying to make your program clearer, then "if break" should definitely be "if broken" |
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Ah, apologies for skipping past it. |
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{if} break {if} considered harmful |
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I can't think of a situation where a variable would change mid-loop without an event, and for that you have event handlers which constantly monitor the state of that event. |
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What [Dub] said - you're basically talking "goto" here, which is kind of frowned upon by many, and is certainly controversial. Maybe it's more convenient in the short-term, but sticking to the loop/while convention isn't all that bad really. |
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You've also got the issue of making sure you know from which loop the break has exited from, if you're scanning through nested x and y indexes in a table structure and want to break out when you've found a search value, how do you know whether you've broken out of your x, or y loop? |
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Personally, I use a boolean value that I set to false prior to the the beginning of my loop, and on a breakable condition, I set it to true. |
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At the end of the loop structure, I test the boolean value and can determine whether I broke out of the loop (and if necessary, which one was broken out of) or if the loop continued to completion. It's not hard. (In fact, this seems to be pretty much what [bigsleep] is talking about a few annos up) |
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On the "goto considered harmful" thing - how about adopting the "comefrom" standard? |
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5760 REM DO NOT DELETE THIS LINE IT IS A TARGET FOR GOTOS |
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//you're basically talking "goto" here// |
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Huh? This is nothing like goto. Transferring control to
an arbitrary point in
the program is completely different from transferring
control to the point
immediately following the current loop. |
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Besides, the idea is nothing more than syntactic sugar—
simply an
abbreviated form of "if( x ) { break; }". As I mentioned
above, Ruby already
has this. I use similar constructions all the time, and
they're tremendously
useful. For example:
# Find every .txt file in path
Find.find( path ) do |file|
next unless File.extname(file) == ".txt"
# Do something with the file here
end
# Find "foo.txt" if it exists in the given path
foo_location = Find.find( path ) { |file| break( file ) if
File.basename( file ) == "foo.txt" }
Which part even remotely resembles a goto statement? |
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I don't know, it all depends on how far you go in before saying something is similar to something else. In terms of a transfer of program flow, then obviously, goto does that, as does break, as do a bunch of other things. Breakif in this context is at least anchored to the end of a loop, so in that respect it's better behaved than a goto might be. I accept that, fair enough. Back in the day, before even break existed, one of the only ways to break out of a loop early was by use of a goto. |
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Similarly in Assembly, going back to the early 80's, there's a bunch of "BRANCH ON" opcodes which are (kind of) equivalent to GOTO IF statements when used within a loop - it would of course be up to the coder to decide how to structure their code, and how far forward past such a loop structure someone might want to branch to, without being handheld by the system by syntactic conventions. And so in that respect, I see that there is a difference between having an additional loop clause that presupposes you will be branching out of it at some stage, and the more "wild-west" approach of allowing goto's all over the place. One's preference will always depend on whether one self-identifies as a cowboy or a sherriff - many people will have been both in their time, hence the cognitive dissonance. |
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// whether one self-identifies as a cowboy or a sherriff // |
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What if one self-identifies as a Mexican bandit ? |
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"Hgotos ... Hwee doan' need no steekning hgotos !" |
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There's a world of difference between a BRANCH embedded in pure Assembler, and the "break;" command - in Assembler, it's up to the programmer to make sure they unwind the stack correctly. |
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If I've understood [akimbomidget] correctly, he is suggesting that you can use 1 breakif statement at the beginning of the loop and it will exit the loop at any point. What everyone else seems to be suggesting is that you can write an if statement to exit at a specific point. |
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[zen_tom] your example is exiting a loop when it has served its purpose eg, do while(searchvalue != currentfield). Also, how do you set your boolean to true? from inside the loop or running parallel threads? Because the former is just an if statement and the latter is slightly above the level of my (and I suspect most others) programming knowledge. |
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[ytk] yours is also just a 'do while' with different syntax |
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Man, I think in autolisp this is the only option you actually have
to simulate an if-then statement.
Not an actual command as far as I know, but that's the logic of it
all. |
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Do this until something is greater than that. If something is
greater than that turn the lights off. |
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If the lights are off, skip this whole next part. (Simplified) |
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[marklar] nothing so clever, obsoive:
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----8<---- 8<---snippety--8<---- 8<----8<------ |
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for (int x = 0; x < max_x; x++ ) {
if (searcharray[x] == findvalue) {
foundit = true;
break;}
}
if (foundit) {
PrintFunction("Found the result!");}
else { // i.e. didn't find it
PrintFunction("sadface");}
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-->8---->8---- >8----snip --->8---- >8---->8-- |
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It is essentially doing what the idea suggests, only using existing syntax, rather than leaning on a new loop-specific construct. |
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I like your idea of using "}broken{" and "}unbroken{" and "}finally{" block syntax. example: |
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for () {
if () break;
} broken {
// activates if 'break' is used
} unbroken{
// activates if 'break' is never used
} finally {
// clean up
} |
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You mind if I make a separate half baked idea using that approach? |
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Also if the above approach is good, well is it a good idea to provide break with a 'return' flag? e.g. "break(flag1)" or "break 1" etc... |
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[zen_tom] if you replace "// i.e. didn't find it
PrintFunction("sadface");}" with 200 lines of code with function calls and all manner of time-consuming crap in each loop, having the ability to break during any part of the loop might be desirable. |
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I'm really playing devil's advocate because as I said in my original comment, I can't see when it would be possible, unless you are doing something so time-consuming that the data has been changed during the loop by another process. But even then, checking variables external to the loop would take even more processing. |
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Actually, is this what happens when you check for database field locking? |
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But what would be the point of the "finally"
construct? It just executes
code whether or not the loop was broken, and after
any resultant
effects. How is that different from just having the
code follow the loop? |
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Anyway, this whole thing is getting a bit silly, IMHO.
The idea can be
summed up as "allow postfix conditionals" and "have
loops return a
value", both of which, as I've pointed out above, are
both already well
known features of Ruby. So if your loop returns
false on break, and non-
false on successful completion (which is effectively
the case with Ruby),
the "broken" and "unbroken" constructs are then
just synonyms for "||"
and "&&", and you're simply using short-circuit
evaluation to determine
which one to run. Congratulations, you've just
reinvented the ?: operator. Of course, since you
can have
break() return an
arbitrary value in Ruby, you can pipe it to a case
statement as above,
and have an unlimited number of potential
"cleanup" actions. |
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Seems to me that every part of this idea has
already been implemented,
and far more thoroughly at that, in at least one
widely-used
programming language. So what's new here? |
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