I love regular expressions
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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 ?
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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
i requested ChatGBT "please write a regular expression which identifies the numerical digits beginning a text ." its response below . ^\d+ is it wrong ? was my request incorrect ?
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If you like to read technical stuff then "Mastering Regular Expressions" by Friedl (yes spelled like that.) Not only interesting but a bit scary since it provides examples that will shut down your system.
thank you for the suggestion . intrguing . too bad i am a cheapskate . as for advanced uses i now am reminded of its use in determining if a number is prime . Demystifying The Regular Expression That Checks If A Number Is Prime – The Codeumentary[^]
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I don't understand why it's difficult - DFA at least. DFA is () [] * + . | That's not a whole lot to master.
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 don't understand why it's difficult - DFA at least.
I am going to answer your question as thoroughly as possible. Regexes are simple in theory, not in practice, which is why people have problems with them. ========================================= In theory, that's all you need to know. In practice, that's just the start - you missed '^' (which has two meanings), '\' (used for escaping those special characters) and '$'. In $PROGRAM, which of the special characters need to be escaped? How about the replacement expression in "%s" (different to the match expression "/s")? How does it match newlines (hint: in Vim, for example, '$' vs '\n' vs '\r do all different things). Write your expression to work in vim, and it fails in your Javascript program. Write your expression in sed and it fails using the regex library in C#. The expression that works in the default invocation of grep fails in the default invocation of Perl. Use `grep -E` and the expression fails on some tools but not on others. Even passing a regex on to an engine is difficult: in an interactive bash shell you'd use sed "s/\\t//g". In a script that sets the results of that invocation to an environment variable you'd use sed "s/\\\\t//g". You run into a similar problems within your programs when you pass around string variables containing regexes, which is why even though many of the programs which use match expressions in their configuration (like nginx) have quoting and escaping rules that differ to the command-line programs which use the same regex library. When you use regex liberally in Python, Bash, Grep, Vim, C#, Perl, Javascript and everything else, you never remember how they all handle the special cases - you have to keep looking them up for that particular program. I'm fairly comfortable with them, having spent the 90s as a Perl programmer, and having used Vim as my default coding editor daily for almost 30 years during which time I collected a couple of postgraduate CS (not IT) degrees (which means I know automata theory better than most), and yet even I have to look regex stuff up on a per-product basis. I am skeptical that you can look at an expression and go "This will work in $x, $y and $z, but not in $a, $b and $c.", and if my skepticism is correct, then you have problems too, but just don't know it. And that is why people have problems with them - you never quite know which contexts allow '.' to
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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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i requested ChatGBT "please write a regular expression which identifies the numerical digits beginning a text ." its response below . ^\d+ is it wrong ? was my request incorrect ?