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New sign at town limits:
MyTown, TX
Estab. 1883
Elev 4500
Pop 5686
Zip 79830
--------------
Total 91899
If you can keep your head while those about you are losing theirs, perhaps you don't understand the situation.
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Now this song is playing in my head: Old Town[^] 
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I got this one: Ghost Town[^]
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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That's a very special one, brings back memories!
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(I'm ignoring backtracking regex here because it's dirty, and algorithmically less useful except for making it easier for the user to match text)
Anyway it's just a tiny functional programming language with only ()|?* 4 explicit operators and 1 implicit one.
Representing the regex programming language as code: Any regex is mathematically equivelent to the DFA state machine it represents, and can be converted algorithmically back and forth to and from a state machine and a regular expression. Perfect compilation/decompilation.
So you can use them to match text (boring!)
Or you can use them to generate code for state machines (less boring!)
And yet I've met a lot of programmers that either loathe them, are intimidated by them, or both.
They're wonderful little things, with interesting mathematical properties, but more importantly, they're useful for everything quick and dirty.
Real programmers use butterflies
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Me think that most of us do not like it, because of bad experience of implementations in the past by different environments...
Almost all of my validations are done in regex, but never done too much of code generations to really use it there...
"The only place where Success comes before Work is in the dictionary." Vidal Sassoon, 1928 - 2012
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If you do it right, regex facilitates rather than hinders code generation but Microsoft's engine is unfortunately limited in that regard. It does code generation, but it doesn't generate C# code for example. It could. It just doesn't.
Like I said in the OP, a regex is a state machine is a regex.
a state machine is code.
it's code all the way down. 
ETA: If you stick to the basic operations and common syntactic sugar and avoid backtracking and other nonsense, most of the regex stuff is the same regardless of implementation.
Real programmers use butterflies
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I very much enjoy Regex.
The complex elegance in a single line of code.
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Have used some regexes in my article Translitera - Phonetic Typing in Some Indian Languages[^], which is a tool for transliterating from English to some Indian languages. The program uses regexes to identify patterns in each word, and hence split each word into manageable parts.
Of course, there are some situations which are not handled, there is always scope for improvement.
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I use them for input validation. Things like dates and times are straightforward. Names are not! Even imposing cultural restrictions (two capitalised names and some fussing around the edges). Patrick O'Reilly-Smythe and Ian McDonald are about as complex as I allowed for members of our Rural Fire Brigade. I can't remember whether Giulio d'Angelo would pass or fail. If he joins up, I'll revisit the code. 
My other major use is in (often throwaway) SED scripts, or of course grep. Things like extracting the word after Invalid user in security logs.
Another one I used recently was to reconstruct words that were hyphenated across lines in a OCR'd manual. Google translate barfs on the fragments of hyphenated words.
Cheers,
Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
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Regex is black magic and sacrifices of caffeine and pizza offered in copious amounts is the only way to appease the beast.
I'm not sure how many cookies it makes to be happy, but so far it's not 27.
JaxCoder.com
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But it's such useful, compelling black magic!
Real programmers use butterflies
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That it is, I've used Expresso Regular Expression Tool[^] for years. It helps but I still can't wrap my head around it. That and dark matter...
I'm not sure how many cookies it makes to be happy, but so far it's not 27.
JaxCoder.com
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Forget backtracking regular expressions, as they don't have the same fancy mathematical properties as their non-backtracking counterparts. Use the non-backtracking operators and there's only 5 operations to remember, concatenation, alternation, parentheses, zero or one match and kleene star (looping * - zero or more match), and concatenation is implicit.
They are
1. Simpler to understand
2. Faster to execute
3. Weirdly mathy but in a cool way
4. The same across almost all regular expression engines
I give a primer at the end of this article. I taught them to my computer, and trust me - it's not very smart, but then I also taught it C in that article.
Fun With State Machines: Incrementally Parsing Numbers Using Hacked Regex[^]
Real programmers use butterflies
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Mike Hankey wrote: dark matter
Dark Matter[^]; great series. A shame it only went three seasons.
Software Zen: delete this;
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It was great right up until that bit where they time-skipped around the future. I could see the downfall of the series coming a mile away.
My current theory is that time-travel, if not baked in from the beginning, is a sign the writers have run out of ideas.
On the other hand, my daughter hates time travel in movies and shows because it's almost always done wrong. The episode where they went back in time was well done, according to her.
Bond
Keep all things as simple as possible, but no simpler. -said someone, somewhere
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I enjoyed the series right up until they were able to insert a little card into their existing engine that allowed them to travel anywhere immediately. I know that FTL is imaginary, but I'd think that "blink" might have required a completely different set of physics requiring a new engine or something. My "willing suspension of disbelief" became unwilling at that point.
Outside of a dog, a book is a man's best friend; inside of a dog, it's too dark to read. -- Groucho Marx
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I would rather use whatever language I am working with to perform the parse. As you just stated... regex is technically another small programming language.
I am not sure if you know this... but you can take a regular expression and use the Ragel state machine compiler[^] to convert it to C/C++, D, Go, Java, Ruby and even Objective-C. Interestingly... I do not see C# support.
Ragel Cheat Sheet[^]
Someone should probably write a little Visual Studio addon that takes a regular expression and converts it to a C# state machine... as it seems .NET programmers use alot of regex.
Best Wishes,
-David Delaune
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Quote: I am not sure if you know this...
I didn't. Thank you for posting it.
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
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I could do that, since I already wrote several apps that do exactly that. The issue is it doesn't support backtracking because i don't like backtracking regex.
Real programmers use butterflies
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regex is a tool.
regex is great when used correctly.
read the owner's manual, as with any tool.
no one should be afraid of using a tool to complete a specific task.
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I am afraid of you, messing up with regex. 
Quote: Or you can use them to generate code for state machines
That's indeed intriguing.
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
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Reminds me of APL. The language of 80's modelling gods. Cryptic enough they had their own department.
At least in assembler we had a few letters for op codes.
Afraid? It's just too forgettable (for me).
It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it.
― Confucian Analects: Rules of Confucius about his food
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