Re: Oddness with regex quantifiers

If you want at most MAX repetitions, use {0,MAX}

The reason for the asymmetry between {MIN,} and {,MAX} is probably that there's a zero in perl, but Inf isn't generally supported.

If you wonder what {,MAX} matches, here's the answer:

$ perl -Mre=debug -ce ' /a{,5}/'
Compiling REx "a{,5}"
Final program:
   1: EXACT <a{,5}> (4)
   4: END (0)
anchored "a{,5}" at 0 (checking anchored isall) minlen 5 
-e syntax OK
Freeing REx: "a{,5}"

$ perl -wE 'say "yes" if "a{,4}" =~ /a{,4}/'
yes

# in contrast:
$ perl -Mre=debug -ce ' /a{0,5}/'
Compiling REx "a{0,5}"
Final program:
   1: CURLY {0,5} (5)
   3:   EXACT <a> (0)
   5: END (0)
minlen 0 
-e syntax OK
Freeing REx: "a{0,5}"
[download]

Perl 6 - second systems done right

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Re^2: Oddness with regex quantifiers by JavaFan (Canon) on Nov 23, 2010 at 23:29 UTC
The reason for the asymmetry between {MIN,} and {,MAX} is probably that there's a zero in perl, but Inf isn't generally supported. The issue was raised not so long ago on p5p, it even caught old farts off guard. I don't think anyone recalled the reason why it does what it does. And people expressed the wish it would have been done otherwise in the past. Some have suggested a warning, but IIRC, nothing happened. It's unlikely the actual meaning is going to change. The advantages of not having to type a 0 don't out-weight the negative impact of potentially breaking code. It's one of the many things that with the benefit of hindsight would have been done differently.	[reply]
Re^3: Oddness with regex quantifiers by talexb (Chancellor) on Nov 24, 2010 at 13:40 UTC
The issue was raised not so long ago on p5p, it even caught old farts off guard. Yeah .. caught this old fart off guard too. Glad to hear I wasn't the only one surprised. :) Alex / talexb / Toronto "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds	[reply]
Re^2: Oddness with regex quantifiers by talexb (Chancellor) on Nov 23, 2010 at 21:36 UTC
The reason for the asymmetry between `{MIN,}` and `{,MAX}` is probably that there's a zero in perl, but Inf isn't generally supported. Hmm .. but isn't the zero implied by the null field? Alex / talexb / Toronto "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds	[reply] [d/l] [select]
Re^3: Oddness with regex quantifiers by moritz (Cardinal) on Nov 23, 2010 at 21:38 UTC
Hmm .. but isn't the zero implied by the null field? Not if you expect `.{MIN,}` to match at least MIN characters. `.{MIN,0}` doesn't make much sense to me. Perl 6 - second systems done right	[reply] [d/l] [select]
Re^3: Oddness with regex quantifiers by elef (Friar) on Nov 23, 2010 at 22:03 UTC
Hmm .. but isn't the zero implied by the null field? Not really, I don't think. If perl accepted {,X}, I'm pretty sure some people would assume that it stood for {1,X}, not {0,X}. After all, one to X matches makes more sense than zero to X matches in many situations. It's propably best to force people to make an explicit choice.	[reply]
Re^4: Oddness with regex quantifiers by ikegami (Patriarch) on Nov 23, 2010 at 22:41 UTC
I'm pretty sure some people would assume that it stood for {1,X}, not {0,X}. That says nothing without an idea of how common such an assumption would be made and an idea of the size of the negative impact making that assumption would entail. one to X matches makes more sense than zero to X matches in many situations. It makes sense in some situations, not necessarily many. It's propably best to force people to make an explicit choice. It's even better not to break backwards compatibility.	[reply]
Re^4: Oddness with regex quantifiers by talexb (Chancellor) on Nov 23, 2010 at 22:14 UTC
Sorry, everyone, I guess I should have said 1, not 0. Alex / talexb / Toronto "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds	[reply]
Re^5: Oddness with regex quantifiers by ikegami (Patriarch) on Nov 23, 2010 at 22:21 UTC
Re^3: Oddness with regex quantifiers by ikegami (Patriarch) on Nov 23, 2010 at 22:01 UTC
`$ perl -E'say "aa" =~ /a{1,}/' 1 $ perl -E'say "aa" =~ /a{1,0}/' Can't do {n,m} with n > m in regex; marked by <-- HERE in m/a{1,0} <-- + HERE / at -e line 1.` [download]	[reply] [d/l]