I love regular expressions
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I blank out on regular expressions. Too much like learning a new language. The other day, I needed to get 0 or more leading characters from a string (as an int). I Googled (regex), I went, I left. Coding challenge: get leading digits (I settled for LINQ)
var text = "123rd NY 2nd Battalion".
//
var count = text.TakeWhile( c => Char.IsDigit( c ) ).Count();
int i = count > 0 ? ConvertToInt32( text.SubString( 0, count) ) : 0;Answer: 123
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
^[0-9]+
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At least the non-backtracking subset. DFA regular expressions. - they are a compact way to describe a simple syntax - they are plain text and brief, easily communicatable and transferable - they are cross platform (at least DFA), running in most any engine - they are incredibly efficient (again, DFA) - they are versatile, able to do validation, tokenization, and matching as well That's probably why they will always be with us. They are maybe the perfect canonical execution of a Chomsky type 3 language. Sure, they can be really terse, but this is as much a strength as it is a weakness, because it facilitates some of the above. I know some people hate them, and I can understand that. But show me a better way.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
i enjoy the challenge of learning / writing regular expressions for my text editing of source code . as in all things mastering it is the same as being invited to perform at Carnegie Hall id est "practice practice practice" . my purpose in this post though is to express my impression from these many and expert posts utilizing fancy schmancy terms of which i do not know which seem to indicate regular expressions are more powerful / advanced / sophisticated than i know as i understand them to be nothing more than a text editing convenience . may i please inquire am i wrong in this regard . thank you kindly .
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i enjoy the challenge of learning / writing regular expressions for my text editing of source code . as in all things mastering it is the same as being invited to perform at Carnegie Hall id est "practice practice practice" . my purpose in this post though is to express my impression from these many and expert posts utilizing fancy schmancy terms of which i do not know which seem to indicate regular expressions are more powerful / advanced / sophisticated than i know as i understand them to be nothing more than a text editing convenience . may i please inquire am i wrong in this regard . thank you kindly .
They're for text processing, but for more than text editing. The C# compiler for example, almost certainly uses a tokenizer built up of regular expressions. That said, you're basically not wrong. I mean, tokenization is almost like text matching, but with a twist.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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Joking aside, more trivially I believe the term "regular" refers to the third level of Chomsky's hierarchy, which, precisely, is defined as Type3-Regular. DFA (Deterministic Finite Automaton) are FSA (Finite State Automaton).
Can confirm.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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A modest proposal: Learn the DFA subset. Commit it to memory, and forget the rest. DFA is the non-backtracking subset of regular expressions () - capture and group [] - match char ranges * - match zero or more + - match one or more ? - match zero or one . - match any single character | - match a or b (a|b)
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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I used ChatGPT precisely for that and it returned a decent regex with an explanation. I needed to word my question in a manner that was generic but the result was actually helpful.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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Not keeping your tool to yourself is one of the leading causes of dismissal, too.
"A little song, a little dance, a little seltzer down your pants" Chuckles the clown
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How the hell would someone know that "[0-9]{1,3}" is enough to find sequential numbers in Microsoft Word? How the hell did I find that magic? Every regular expression seems to require a convoluted google search. Crazy world...
Our Forgotten Astronomy | Object Oriented Programming with C++ | Wordle solver
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A modest proposal: Learn the DFA subset. Commit it to memory, and forget the rest. DFA is the non-backtracking subset of regular expressions () - capture and group [] - match char ranges * - match zero or more + - match one or more ? - match zero or one . - match any single character | - match a or b (a|b)
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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cool. forgot chatgpt is hanging out there
"A little time, a little trouble, your better day" Badfinger
I had exactly the dilemna you had - I was looking for a reverse regular expression parser i.e. create a regular expression from a desired result and an initial string and I thought I would give ChatGPT a go.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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would not ? match zero or one not be part of that? or is that a posix extension?
"A little song, a little dance, a little seltzer down your pants" Chuckles the clown
You're right. Totally spaced that I edited.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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jschell wrote:
Not sure what you mean by that.
What I mean is that regardless of the platform you choose, there is a way to run a DFA regular expression on it. And yeah, that encompasses many different engines, which themselves are what run on a particular platform, unless you're doing code generation, which I do sometimes for them so I don't have to include the regex engine in my firmware. That code is easy to make cross platform. You'd almost have to put in extra effort to make it otherwise. :) I was maybe trying to be too brief by half. I assumed the meaning would come through, but I guess not.
jschell wrote:
Perhaps you were referring to that the simplest syntax works in different engines though
In part yes, but also, virtually every platform has a DFA regex engine for it, or alternatively you can generate DFA code for that platform, with something such as my rxcg project. I was intending to imply that as well.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
honey the codewitch wrote:
What I mean is that regardless of the platform you choose, there is a way to run a DFA regular expression on it.
If you find a programming system that doesn't allow that then you might prepare for the universe to end. Far as I can recall it would be mathematically impossible for that not to be true.
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I recall this too. Qwerty I heard was in part laid out to slow typists down so the mechanical typewriter could keep up. I heard it from the Beagle Bros back in the 1980s so I don't know how true it is. Either way, presumably eventually that wasn't an issue anymore. And Devorak was a common alternative, or at least common as qwerty alternatives go. It was touted as better, but despite the hype I remember reading that it didn't actually improve people's WPM.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
honey the codewitch wrote:
out to slow typists down so the mechanical typewriter could keep up
Not exactly. Rather the layout exists to allow typing to be faster. QWERTY - Wikipedia[^] "but rather to speed up typing. Indeed, there is evidence that, aside from the issue of jamming, placing often-used keys farther apart increases typing speed, because it encourages alternation between the hands."
honey the codewitch wrote:
but despite the hype
I believe that was the one where the data was faked.
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honey the codewitch wrote:
What I mean is that regardless of the platform you choose, there is a way to run a DFA regular expression on it.
If you find a programming system that doesn't allow that then you might prepare for the universe to end. Far as I can recall it would be mathematically impossible for that not to be true.
jschell wrote:
If you find a programming system that doesn't allow that then you might prepare for the universe to end
Maybe I misunderstand you, but if you're speaking in the general sense, you aren't going to run a garbage collected system for example, on an 8-bit platform with 4KB of RAM, hopefully. Even if you could, it wouldn't be practical for anything. A DFA on the other hand will run handily there.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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jschell wrote:
If you find a programming system that doesn't allow that then you might prepare for the universe to end
Maybe I misunderstand you, but if you're speaking in the general sense, you aren't going to run a garbage collected system for example, on an 8-bit platform with 4KB of RAM, hopefully. Even if you could, it wouldn't be practical for anything. A DFA on the other hand will run handily there.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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i enjoy the challenge of learning / writing regular expressions for my text editing of source code . as in all things mastering it is the same as being invited to perform at Carnegie Hall id est "practice practice practice" . my purpose in this post though is to express my impression from these many and expert posts utilizing fancy schmancy terms of which i do not know which seem to indicate regular expressions are more powerful / advanced / sophisticated than i know as i understand them to be nothing more than a text editing convenience . may i please inquire am i wrong in this regard . thank you kindly .
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honey the codewitch wrote:
A DFA on the other hand will run handily there.
Reverse that though. What system, which has resources to run anything that is non-trivial, will not run a DFA?
I can't think of anything that couldn't run a DFA. :confused: It's such a basic Turing-esque construction.
Check out my IoT graphics library here: https://honeythecodewitch.com/gfx And my IoT UI/User Experience library here: https://honeythecodewitch.com/uix
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Richard Attenborough : Actor, Jurasic Park, The Great Escape ... David Attenbourogh: Broadcaster and Biologist They are brothers, though. But maybe you meant Richard?
"A little song, a little dance, a little seltzer down your pants" Chuckles the clown
Yeah, I meant the one who narrates nature programs.
I’ve given up trying to be calm. However, I am open to feeling slightly less agitated. I’m begging you for the benefit of everyone, don’t be STUPID.
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need regex to natural language and vice versa
"A little time, a little trouble, your better day" Badfinger
This alleged AI-powered generator got me close to what I needed today: https://www.regexgo.com/[^] And this site was a great help in troubleshooting and refining the AI's results: https://regex101.com/[^] Bonus: I still don't understand RegEx.
There are no solutions, only trade-offs.
- Thomas SowellA day can really slip by when you're deliberately avoiding what you're supposed to do.
- Calvin (Bill Watterson, Calvin & Hobbes) -
I'm absolutely with you on that. Also, with PCREs, the /x switch allows you to indent and comment to your heart's content, so you can write perfectly legible code, and there are on-line engines where you can drop your expression and your input and watch step by step while it does its magic. I'm not sure that I do a day's work without writing a regex and I know of no tool with anywhere near the power for parsing text. ~~~~~~~~ <°}}}>«<
what about AWK ?