Re: reverse scanner
Well, after more testing, I found that my first version (labelled frontal
attack) doesn't always work. Just in case anyone other than me cares, here's
a new version that seems to work properly. Sorry for the noise.
Boyd
// frontal attack
// testString = @0756013;
testString = @4756013;
// testString = @0756;
// testString = @0;
// alleles and digitsPerAllele are passed as arguments; the values shown
here are just for testing
int alleles = 3;
NSUInteger digitsPerAllele = 3;
NSString *subString;
NSRange range;
int theInt;
int i;
int sLength = [testString length];
range.location = 0;
int remainder = [testString length] % digitsPerAllele;
if (remainder 0) {
range.length = remainder;
subString = [testString substringWithRange:range];
theInt = [subString intValue];
--alleles;
range.location = remainder;
sLength = sLength - remainder;
}
if (sLength 0) {
range.length = digitsPerAllele;
for (i = 0; i alleles; i++ ) {
subString = [testString substringWithRange:range];
theInt = [subString intValue];
range.location += digitsPerAllele;
}
}
Begin forwarded message:
From: Boyd Collier bcolli...@cox.net
Subject: Re: reverse scanner
Date: August 12, 2013 1:00:56 PM PDT
To: Cocoa Dev List cocoa-dev@lists.apple.com
I've come up with a couple of reasonably straight-forward solutions to my
problem, but first, thanks to everyone who offered suggestions. Even though I
didn't choose to use them, your willingness to make them is definitely
appreciated.
Here are my solutions (note that there are 2, one labelled attack from the
rear, the other labelled frontal attack). I won't claim that they have
been really thoroughly tested, but I have tried a variety of values for
testString, d, digitsPerAllele and alleles and both methods appear to work.
If anyone sees a problem or an improvements, please let me know. Right now,
I favor the frontal attack, which occurred to me in the middle of the night
-- I seldom have reason to use the % operator and so didn't think of it right
away. Of course, in actual use, I'll first take steps to separate the string
that's being processed into substrings, if the original string uses a ;
(for example) to separate allelic values, e.g. if the string being processed
is 04;756;013.
NSString *testString = @0756013;
NSUInteger d = 3;
NSUInteger digitsPerAllele = d;
NSUInteger alleles = 3;
NSString *subString;
NSRange range;
int theInt;
// attack from the rear
int startOfRange = [testString length];
int length = d;
int i;
for (i = 0; i alleles; i++ ) {
startOfRange = startOfRange-d;
if (startOfRange 0) {
length = length + startOfRange; // note that startOfRange is
negative here
if (length = 0)
break;
startOfRange = 0;
d = length;
}
range.location = startOfRange;
range.length = d;
subString = [testString substringWithRange:range];
theInt = [subString intValue];
}
// frontal attack
testString = @04756013;
int remainder = [testString length] % digitsPerAllele;
range.location = 0;
range.length = remainder;
subString = [testString substringWithRange:range];
theInt = [subString intValue];
--alleles;
range.location = remainder;
range.length = digitsPerAllele;
for (i = 0; i alleles; i++ ) {
subString = [testString substringWithRange:range];
theInt = [subString intValue];
range.location += digitsPerAllele;
}
On Aug 10, 2013, at 10:07 AM, Boyd Collier bcolli...@cox.net wrote:
I'm dealing with a situation in which I have to scan strings that are
separated by tabs, and for each string, I have to extract two numerical
values, with these values being separated by a non-numerical character or
not being separated by any character at all. I know the maximum number of
characters used to represent each number, but unfortunately, the first
character in the group of characters used to represent the first number can,
quite arbitrarily, be either a 0 or missing. For example, with the number
of characters used to represent each number known to be 2, the strings 607,
0607, 06;07 (note the semicolon between 06 and 07) should all result in 6
and 7 being extracted as the two numerical values. Of course, I'd like to do
something simple, and were it not for the arbitrary inclusion of a leading
0, it would be quite simple to use an instance of NSScanner. Or, if there
were such a beast as NSReverseScanner, it would also be relatively straight
forward, but so far as I'm aware, no such beast exists. I can think of a
couple
Re: reverse scanner
I've come up with a couple of reasonably straight-forward solutions to my
problem, but first, thanks to everyone who offered suggestions. Even though I
didn't choose to use them, your willingness to make them is definitely
appreciated.
Here are my solutions (note that there are 2, one labelled attack from the
rear, the other labelled frontal attack). I won't claim that they have been
really thoroughly tested, but I have tried a variety of values for testString,
d, digitsPerAllele and alleles and both methods appear to work. If anyone sees
a problem or an improvements, please let me know. Right now, I favor the
frontal attack, which occurred to me in the middle of the night -- I seldom
have reason to use the % operator and so didn't think of it right away. Of
course, in actual use, I'll first take steps to separate the string that's
being processed into substrings, if the original string uses a ; (for
example) to separate allelic values, e.g. if the string being processed is
04;756;013.
NSString *testString = @0756013;
NSUInteger d = 3;
NSUInteger digitsPerAllele = d;
NSUInteger alleles = 3;
NSString *subString;
NSRange range;
int theInt;
// attack from the rear
int startOfRange = [testString length];
int length = d;
int i;
for (i = 0; i alleles; i++ ) {
startOfRange = startOfRange-d;
if (startOfRange 0) {
length = length + startOfRange; // note that startOfRange is
negative here
if (length = 0)
break;
startOfRange = 0;
d = length;
}
range.location = startOfRange;
range.length = d;
subString = [testString substringWithRange:range];
theInt = [subString intValue];
}
// frontal attack
testString = @04756013;
int remainder = [testString length] % digitsPerAllele;
range.location = 0;
range.length = remainder;
subString = [testString substringWithRange:range];
theInt = [subString intValue];
--alleles;
range.location = remainder;
range.length = digitsPerAllele;
for (i = 0; i alleles; i++ ) {
subString = [testString substringWithRange:range];
theInt = [subString intValue];
range.location += digitsPerAllele;
}
On Aug 10, 2013, at 10:07 AM, Boyd Collier bcolli...@cox.net wrote:
I'm dealing with a situation in which I have to scan strings that are
separated by tabs, and for each string, I have to extract two numerical
values, with these values being separated by a non-numerical character or not
being separated by any character at all. I know the maximum number of
characters used to represent each number, but unfortunately, the first
character in the group of characters used to represent the first number can,
quite arbitrarily, be either a 0 or missing. For example, with the number of
characters used to represent each number known to be 2, the strings 607,
0607, 06;07 (note the semicolon between 06 and 07) should all result in 6 and
7 being extracted as the two numerical values. Of course, I'd like to do
something simple, and were it not for the arbitrary inclusion of a leading 0,
it would be quite simple to use an instance of NSScanner. Or, if there were
such a beast as NSReverseScanner, it would also be relatively straight
forward, but so far as I'm aware, no such beast exists. I can think of a
couple of ways do accomplish this task, but if someone has already come up
with a clean way of scanning in reverse, I'd appreciate hearing from them.
Boyd
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reverse scanner
I'm dealing with a situation in which I have to scan strings that are separated by tabs, and for each string, I have to extract two numerical values, with these values being separated by a non-numerical character or not being separated by any character at all. I know the maximum number of characters used to represent each number, but unfortunately, the first character in the group of characters used to represent the first number can, quite arbitrarily, be either a 0 or missing. For example, with the number of characters used to represent each number known to be 2, the strings 607, 0607, 06;07 (note the semicolon between 06 and 07) should all result in 6 and 7 being extracted as the two numerical values. Of course, I'd like to do something simple, and were it not for the arbitrary inclusion of a leading 0, it would be quite simple to use an instance of NSScanner. Or, if there were such a beast as NSReverseScanner, it would also be relatively straight forward, but so far as I'm aware, no such beast exists. I can think of a couple of ways do accomplish this task, but if someone has already come up with a clean way of scanning in reverse, I'd appreciate hearing from them. Boyd ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
Is there a problem with using a character set of all digits except 0 when recognizing digits? -- Gary L. Wade (Sent from my iPad) http://www.garywade.com/ On Aug 10, 2013, at 10:07 AM, Boyd Collier bcolli...@cox.net wrote: I'm dealing with a situation in which I have to scan strings that are separated by tabs, and for each string, I have to extract two numerical values, with these values being separated by a non-numerical character or not being separated by any character at all. I know the maximum number of characters used to represent each number, but unfortunately, the first character in the group of characters used to represent the first number can, quite arbitrarily, be either a 0 or missing. For example, with the number of characters used to represent each number known to be 2, the strings 607, 0607, 06;07 (note the semicolon between 06 and 07) should all result in 6 and 7 being extracted as the two numerical values. Of course, I'd like to do something simple, and were it not for the arbitrary inclusion of a leading 0, it would be quite simple to use an instance of NSScanner. Or, if there were such a beast as NSReverseScanner, it would also be relatively straight forward, but so far as I'm aware, no such beast exists. I can think of a couple of ways do accomplish this task, but if someone has already come up with a clean way of scanning in reverse, I'd appreciate hearing from them. Boyd ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
On 2013 Aug 10, at 10:07, Boyd Collier bcolli...@cox.net wrote: but if someone has already come up with a clean way of scanning in reverse In Mac OS X 10.7+, we have NSRegularExpression. In earlier systems, call out to Perl. Regexes are fun. ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
Heh, I’d actually argue that NSScanner is a much much better API to use here (and in fact nearly everywhere). Regular expressions constrain you only to regular grammars, which are a pretty small set. In my experience 99% of the use of them is actually trying to parse something that’s not *quite* a regular grammar, and uses a hack on top of regular expressions to do something not-quite-right. NSScanner by comparison makes the separation of what’s scanning/tokenisation, and what’s up to your (turing complete) program much more clear. So basically, (at least in my opinion), if you want to parse something that’s regular, NSScanner is a great choice. If you want to parse something that’s context free, look at CoreParse (Not tooting my own horn, honest). And finally, if you want to parse something that’s more even than that, then you’re probably back to NSScanner and a turing complete program. About the only use for regular expressions I can think of is asking NSScanner to scan something that it doesn’t by default know about. Tom Davie On 10 Aug 2013, at 19:53, Jerry Krinock je...@ieee.org wrote: On 2013 Aug 10, at 10:07, Boyd Collier bcolli...@cox.net wrote: but if someone has already come up with a clean way of scanning in reverse In Mac OS X 10.7+, we have NSRegularExpression. In earlier systems, call out to Perl. Regexes are fun. ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/tom.davie%40gmail.com This email sent to tom.da...@gmail.com ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
If one number has a leading leading zero will the other number have one, if applicable? For instance, is 60 followed by 7 distinguishable from 6 followed by 07? Sandor Szatmari On Aug 10, 2013, at 13:07, Boyd Collier bcolli...@cox.net wrote: I'm dealing with a situation in which I have to scan strings that are separated by tabs, and for each string, I have to extract two numerical values, with these values being separated by a non-numerical character or not being separated by any character at all. I know the maximum number of characters used to represent each number, but unfortunately, the first character in the group of characters used to represent the first number can, quite arbitrarily, be either a 0 or missing. For example, with the number of characters used to represent each number known to be 2, the strings 607, 0607, 06;07 (note the semicolon between 06 and 07) should all result in 6 and 7 being extracted as the two numerical values. Of course, I'd like to do something simple, and were it not for the arbitrary inclusion of a leading 0, it would be quite simple to use an instance of NSScanner. Or, if there were such a beast as NSReverseScanner, it would also be relatively straight forward, but so far as I'm aware, no such beast exists. I can think of a couple of ways do accomplish this task, but if someone has already come up with a clean way of scanning in reverse, I'd appreciate hearing from them. Boyd ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/admin.szatmari.net%40gmail.com This email sent to admin.szatmari@gmail.com ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
On Aug 10, 2013, at 12:17 PM, Tom Davie wrote: Heh, I’d actually argue that NSScanner is a much much better API to use here (and in fact nearly everywhere). Regular expressions constrain you only to regular grammars, which are a pretty small set. In my experience 99% of the use of them is actually trying to parse something that’s not *quite* a regular grammar, and uses a hack on top of regular expressions to do something not-quite-right. NSScanner by comparison makes the separation of what’s scanning/tokenisation, and what’s up to your (turing complete) program much more clear. So basically, (at least in my opinion), if you want to parse something that’s regular, NSScanner is a great choice. If you want to parse something that’s context free, look at CoreParse (Not tooting my own horn, honest). And finally, if you want to parse something that’s more even than that, then you’re probably back to NSScanner and a turing complete program. About the only use for regular expressions I can think of is asking NSScanner to scan something that it doesn’t by default know about. I would agree that NSScanner is a better API than NSRegularExpression, but I think that is Apple's fault because there are better regex API's, such as RegexKit. I would argue, however, that it is NSScanner that only functions well with fixed and unvarying grammars and has no context, other than a specific, unvarying linear progression. Regular expressions have a huge grammar and when you consider conditionals and zero-width assertions you can parse information that would send NSScanner into dizzying fits. Not to mention that NSScanner can't even touch the problem that the OP is experiencing, while regular expressions will handle it very nicely. On 10 Aug 2013, at 19:53, Jerry Krinock je...@ieee.org wrote: On 2013 Aug 10, at 10:07, Boyd Collier bcolli...@cox.net wrote: but if someone has already come up with a clean way of scanning in reverse In Mac OS X 10.7+, we have NSRegularExpression. In earlier systems, call out to Perl. Regexes are fun. Keary Suska Esoteritech, Inc. Demystifying technology for your home or business ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
On 10 Aug 2013, at 22:44, Keary Suska cocoa-...@esoteritech.com wrote: On Aug 10, 2013, at 12:17 PM, Tom Davie wrote: Heh, I’d actually argue that NSScanner is a much much better API to use here (and in fact nearly everywhere). Regular expressions constrain you only to regular grammars, which are a pretty small set. In my experience 99% of the use of them is actually trying to parse something that’s not *quite* a regular grammar, and uses a hack on top of regular expressions to do something not-quite-right. NSScanner by comparison makes the separation of what’s scanning/tokenisation, and what’s up to your (turing complete) program much more clear. So basically, (at least in my opinion), if you want to parse something that’s regular, NSScanner is a great choice. If you want to parse something that’s context free, look at CoreParse (Not tooting my own horn, honest). And finally, if you want to parse something that’s more even than that, then you’re probably back to NSScanner and a turing complete program. About the only use for regular expressions I can think of is asking NSScanner to scan something that it doesn’t by default know about. I would agree that NSScanner is a better API than NSRegularExpression, but I think that is Apple's fault because there are better regex API's, such as RegexKit. I would argue, however, that it is NSScanner that only functions well with fixed and unvarying grammars and has no context, other than a specific, unvarying linear progression. Regular expressions have a huge grammar and when you consider conditionals and zero-width assertions you can parse information that would send NSScanner into dizzying fits. Not to mention that NSScanner can't even touch the problem that the OP is experiencing, while regular expressions will handle it very nicely. No, some hacked on extensions to regular expressions can do this. Because people keep repeatedly bumping into the problem that they’re not as powerful as CFGs, and most parsing problems aren’t regular. Tom Davie ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
On 10 Aug 2013, at 3:54 PM, Tom Davie tom.da...@gmail.com wrote: On 10 Aug 2013, at 22:44, Keary Suska cocoa-...@esoteritech.com wrote: No, some hacked on extensions to regular expressions can do this. Because people keep repeatedly bumping into the problem that they’re not as powerful as CFGs, and most parsing problems aren’t regular. See no true Scotsman. http://en.wikipedia.org/wiki/No_true_Scotsman The point remains that there are quite powerful extensions to the formal regular-expression syntax that are reliable, in almost universal use, and helpful to the OP. In your heart of hearts, you will admit to knowing that. In the '80s, I called myself a hacker, and even had a vanity license plate MAC HAKR. The battle over the popular meaning of hacker has been lost, and so it has been with regular expression. — F ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
Are you numbers constrained to be from 1 to 9? How about 0677 (which is actually 6 and 7) or 0607 (which is actually 607) etc? Phil On Aug 10, 2013, at 2:54 PM, Tom Davie tom.da...@gmail.com wrote: On 10 Aug 2013, at 22:44, Keary Suska cocoa-...@esoteritech.com wrote: On Aug 10, 2013, at 12:17 PM, Tom Davie wrote: Heh, I’d actually argue that NSScanner is a much much better API to use here (and in fact nearly everywhere). Regular expressions constrain you only to regular grammars, which are a pretty small set. In my experience 99% of the use of them is actually trying to parse something that’s not *quite* a regular grammar, and uses a hack on top of regular expressions to do something not-quite-right. NSScanner by comparison makes the separation of what’s scanning/tokenisation, and what’s up to your (turing complete) program much more clear. So basically, (at least in my opinion), if you want to parse something that’s regular, NSScanner is a great choice. If you want to parse something that’s context free, look at CoreParse (Not tooting my own horn, honest). And finally, if you want to parse something that’s more even than that, then you’re probably back to NSScanner and a turing complete program. About the only use for regular expressions I can think of is asking NSScanner to scan something that it doesn’t by default know about. I would agree that NSScanner is a better API than NSRegularExpression, but I think that is Apple's fault because there are better regex API's, such as RegexKit. I would argue, however, that it is NSScanner that only functions well with fixed and unvarying grammars and has no context, other than a specific, unvarying linear progression. Regular expressions have a huge grammar and when you consider conditionals and zero-width assertions you can parse information that would send NSScanner into dizzying fits. Not to mention that NSScanner can't even touch the problem that the OP is experiencing, while regular expressions will handle it very nicely. No, some hacked on extensions to regular expressions can do this. Because people keep repeatedly bumping into the problem that they’re not as powerful as CFGs, and most parsing problems aren’t regular. Tom Davie ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/ershler%40cvrti.utah.edu This email sent to ersh...@cvrti.utah.edu Philip R. Ershler Ph.D. University of Utah Cardiovascular Research and Training Institute 95 South 2000 East Salt Lake City, UT 84112-5000 phone: (801) 230-8771 alt ph: (801) 587-9528 fax: (801) 581-3128 e-mail: ersh...@cvrti.utah.edu ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
Whoops, I meant Are you numbers constrained to be from 1 to 9? How about 0677 (which is actually 6 and 77) or 0607 (which is actually 607) etc? Phil On Aug 10, 2013, at 2:54 PM, Tom Davie tom.da...@gmail.com wrote: On 10 Aug 2013, at 22:44, Keary Suska cocoa-...@esoteritech.com wrote: On Aug 10, 2013, at 12:17 PM, Tom Davie wrote: Heh, I’d actually argue that NSScanner is a much much better API to use here (and in fact nearly everywhere). Regular expressions constrain you only to regular grammars, which are a pretty small set. In my experience 99% of the use of them is actually trying to parse something that’s not *quite* a regular grammar, and uses a hack on top of regular expressions to do something not-quite-right. NSScanner by comparison makes the separation of what’s scanning/tokenisation, and what’s up to your (turing complete) program much more clear. So basically, (at least in my opinion), if you want to parse something that’s regular, NSScanner is a great choice. If you want to parse something that’s context free, look at CoreParse (Not tooting my own horn, honest). And finally, if you want to parse something that’s more even than that, then you’re probably back to NSScanner and a turing complete program. About the only use for regular expressions I can think of is asking NSScanner to scan something that it doesn’t by default know about. I would agree that NSScanner is a better API than NSRegularExpression, but I think that is Apple's fault because there are better regex API's, such as RegexKit. I would argue, however, that it is NSScanner that only functions well with fixed and unvarying grammars and has no context, other than a specific, unvarying linear progression. Regular expressions have a huge grammar and when you consider conditionals and zero-width assertions you can parse information that would send NSScanner into dizzying fits. Not to mention that NSScanner can't even touch the problem that the OP is experiencing, while regular expressions will handle it very nicely. No, some hacked on extensions to regular expressions can do this. Because people keep repeatedly bumping into the problem that they’re not as powerful as CFGs, and most parsing problems aren’t regular. Tom Davie ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/ershler%40cvrti.utah.edu This email sent to ersh...@cvrti.utah.edu Philip R. Ershler Ph.D. University of Utah Cardiovascular Research and Training Institute 95 South 2000 East Salt Lake City, UT 84112-5000 phone: (801) 230-8771 alt ph: (801) 587-9528 fax: (801) 581-3128 e-mail: ersh...@cvrti.utah.edu ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/ershler%40cvrti.utah.edu This email sent to ersh...@cvrti.utah.edu ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: reverse scanner
NSScanner is *not* a parser - it is a lexical analyser and you are the one that is responsible of writing a parser on top of it. I have a project Subtitler (http://github.com/xcvista/Subtitler) that included 2 parsers that is built on top of NSScanner, and I vaguely remember that there is an Smalltalk compiler written in Objective-C using NSScanner extensively as its lexer and LLVM as code emitter somewhere... On Aug 11, 2013, at 4:44, Keary Suska cocoa-...@esoteritech.com wrote: On Aug 10, 2013, at 12:17 PM, Tom Davie wrote: Heh, I’d actually argue that NSScanner is a much much better API to use here (and in fact nearly everywhere). Regular expressions constrain you only to regular grammars, which are a pretty small set. In my experience 99% of the use of them is actually trying to parse something that’s not *quite* a regular grammar, and uses a hack on top of regular expressions to do something not-quite-right. NSScanner by comparison makes the separation of what’s scanning/tokenisation, and what’s up to your (turing complete) program much more clear. So basically, (at least in my opinion), if you want to parse something that’s regular, NSScanner is a great choice. If you want to parse something that’s context free, look at CoreParse (Not tooting my own horn, honest). And finally, if you want to parse something that’s more even than that, then you’re probably back to NSScanner and a turing complete program. About the only use for regular expressions I can think of is asking NSScanner to scan something that it doesn’t by default know about. I would agree that NSScanner is a better API than NSRegularExpression, but I think that is Apple's fault because there are better regex API's, such as RegexKit. I would argue, however, that it is NSScanner that only functions well with fixed and unvarying grammars and has no context, other than a specific, unvarying linear progression. Regular expressions have a huge grammar and when you consider conditionals and zero-width assertions you can parse information that would send NSScanner into dizzying fits. Not to mention that NSScanner can't even touch the problem that the OP is experiencing, while regular expressions will handle it very nicely. On 10 Aug 2013, at 19:53, Jerry Krinock je...@ieee.org wrote: On 2013 Aug 10, at 10:07, Boyd Collier bcolli...@cox.net wrote: but if someone has already come up with a clean way of scanning in reverse In Mac OS X 10.7+, we have NSRegularExpression. In earlier systems, call out to Perl. Regexes are fun. Keary Suska Esoteritech, Inc. Demystifying technology for your home or business ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/xcvista%40me.com This email sent to xcvi...@me.com ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
