Regular Expressions in 100 lines of Scala

http://rcoh.svbtle.com/no-magic-regular-expressions

by rusbus • 12 years ago

40 21 12 years ago

rcoh.svbtle.com

hello_there• 12 years ago

It's not so easy to see in the linked article, but the article is actually in 3 parts:

Part 1: http://rcoh.svbtle.com/no-magic-regular-expressions

Part 2: http://rcoh.svbtle.com/regular-expressions-part-2

Part 3: http://rcoh.svbtle.com/no-magic-regular-expressions-part-3

It's really well done!

zerr2• 12 years ago

Btw, is Scala still relevant with the coming of Java 9?

ARussell• 12 years ago

I definitely think so. Why wouldn't it be? Do you think Java 8 or 9 would be able to solve OP's problem with as much expressiveness as Scala?

zerr2• 12 years ago

Not completely, but there was/is a line of advising to use Scala as a better Java. Java is getting better and better with subsequent versions, so at least this line of Scala loses strength I believe.

broodbucket• 12 years ago

Another factor is that Scala runs on JRE 6 and 7. There's still a huge amount of Java 6 in production environments, and much much less Java 8.

lmm2• 12 years ago

Java is improving, but it's got a long, long way to go before it can catch Scala. Can you write data types in Java 9 as simply as case classes? Does type inference just work? Is there something as concise as pattern matching? Does it have typeclasses, or an equivalent solution to the expression problem? Can you write DSLs with the flexibility of Scala's for syntax? Can you write tagged types? Even if it has all these features, does it have them in a unified way, implemented by consistently combining some simple primitives, or is it a mess of special cases?

zak_mc_kracken• 12 years ago

Considering that Java still has about 95% market share on the JVM, I'd say Scala has a long way to go before it can catch up to Java. Same observation for jobs and tooling.

It really all depends on what criterion you use.

caoilte• 12 years ago

You're asking that question about two years too early.

bshimmin• 12 years ago

The title is a little misleading - perhaps better would be "A very limited subset of Regular Expressions in 100 lines of Scala".

While the code is concise, this is more a case of "it implements A and B of an X" than "it implements an X, apart from A and B".

Still, all three parts of the series are a good read, and definitely helpful for learning about parsing and about Scala.

peq• 12 years ago

Regular expressions just need 3 things: sequence, alternatives (|), and repetition(*). Everything else is an extension.

tel• 12 years ago

And the empty versions/identities of those operations

brudgers• 12 years ago

Mathematically, regular expressions are limited in comparison to what are commonly called 'regular expressions' or 'regexes' by programmers. Mathematical regular expressions can be translated into automata, 'Regex style regular expressions' often cannot.

The advantage of mathematical regular expressions is that they terminate in O(n) time based on the length of the input string. The disadvantage is that they lack features like capture groups and look ahead/behind. The important point is that engines like those of Perl or Java are not based on regular expressions in a mathematical sense. This is true of any Regex engine that stores state or backtracks.

hyp0• 12 years ago

Regular Expressions in 100 lines of Scala

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