Comments on: Tools of the Effective Developer: Regular Expressions

By: Patrick

Patrick — Thu, 20 May 2010 21:05:50 +0000

@RJ ever seen http://txt2re.com/ ?

By: deeringc

deeringc — Tue, 18 May 2010 14:12:46 +0000

It’s actually much much worse for email matching if you want full compliance with RFC822.

Beware: http://www.ex-parrot.com/~pdw/Mail-RFC822-Address.

By: Hans-Eric

Hans-Eric — Sat, 15 May 2010 08:27:08 +0000

@Joep
Absolutely, regular expressions originates from automata theory so if you want to master them you need to go to the NDA level. However, for the problems I usually deal with, thinking in terms of string patterns is quite enough. But then again, in the face of a more complicated expression I’m usually lost. Hm, next time that happens to me I think I’ll take your advice and visualize the problem with a state diagram
Thank you for your comment.

By: Joep

Joep — Fri, 14 May 2010 07:18:50 +0000

I prefer to think of Regexes as state-machines, or more specifically nondeterministic state machines. http://en.wikipedia.org/wiki/Nondeterministic_finite_state_machine

If you understand what an NDFA IS, I think regex becomes far easier to comprehend and use effectively.

By: Hans-Eric

Hans-Eric — Thu, 13 May 2010 21:35:02 +0000

@cowardlydragon Totally agree. Validating e-mail addresses is a good example of regexps failing to provide a perfect solution. And being "self-obfuscating" is the reason why it's important to document the behavior, i.e. with comments.

By: cowardlydragon

cowardlydragon — Thu, 13 May 2010 20:49:54 +0000

The #1 to remember about regular expressions is that they can solve the obvious use case of many problems, but once edge cases crop up, regular expressions lack the computational flexibility to handle them.

They are also self-obfuscating.

However, they are undeniably useful.

By: Hans-Eric

Hans-Eric — Thu, 13 May 2010 08:49:04 +0000

@RJ
Ah yes, I know what you mean. However, I tend to use them often enough so that at least the basics sticks.
A regex expert for hire site? That could fly

By: RJ

RJ — Thu, 13 May 2010 01:28:13 +0000

The thing that drives me nuts about regular expressions is that I hardly ever use them. I just don’t need to in 99% of my programming.

However in that 1% when I do need them it invariably results in me going to one of the various “Introduction to Regex” sites and re-learning what I need to know and an hour or so of regular expressions.

Maybe someone needs to create a paid for site where you submit what you need and get a regex back ;~)

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