5 ms·

I prefer fishbowl's law Every regexp that you apply to a particular block of text reduces the applicability of regular expressions by an order of magnit

by brehaut 16y ago

I prefer fishbowl's law Every regexp that you apply to a particular block of text reduces the applicability of regular expressions by an order of magnitude. - http://fishbowl.pastiche.org/2003/08/18/beware_regular_expressions/ http://fishbowl.pastiche.org/2003/08/18/beware_regular_expre... The minimum any programmer needs to know about regexps is when they are applicable, and more importantly, when they are not.

philwelch 16y ago
Your link advocates writing parsers in situations where regexes aren't powerful enough, which is quite sensible and even quite practical in some cases. But there's a big reason regexes are overused compared to parsers--regex engines come stock in most programming languages, and parser generators don't. There's a big mismatch in complexity between overusing something the language gives you for free and building in a parser. Perl 6 deserves some credit for their "rules" system, which can actually take a grammar and parse from it.
- brehaut 16y ago
  Agreed, the impedance of parsers has traditionally been much higher than for regexps. However, a lot of languages now have some sort of parse combinator library which dramatically increases the ease of writing a parser. I'm thinking specifically of the Parsec inspired family, which has implementations or derivations in many common languages, even C# and Java (despite being noticably more cumbersome in those cases there). [I cannot speak for perl 6, but i trust you are correct]
brehaut 16y ago
Seeing how im advocating that everyone should know when to be using parsing tools rather than cobbling together a regexp cludge, here are some links to some relevant tools in a variety of languages. Note that these are not parser generator tools, but parser combinator libraries: * Python: PyParsing - http://pyparsing.wikispaces.com/ - this is probably the most well respected parser library for python picoparse - http://github.com/brehaut/picoparse - My parsec inspired parser combinator library. It is significantly more light weight than pyparsing, and I would recommend pyparsing in its place for more heavy lifting parsers. * Ruby: RParsec - http://rubyforge.org/projects/rparsec/ - A ruby implementation of Parsec. I've heard good things about it. * Haskell: Parsec - http://legacy.cs.uu.nl/daan/parsec.html - This is an amazing library, worth anyones time. http://book.realworldhaskell.org/read/using-parsec.html http://www.haskell.org/haskellwiki/Parsec * F#: FParsec - http://www.quanttec.com/fparsec/ - This is reason enough to learn F#; it is a fairly true port of the haskell library and very nice to use. * Scala: Packrat Parsing - I believe this is part of the standard lib. http://www.scala-lang.org/docu/files/api/scala/util/parsing/combinator/PackratParsers.html * Clojure: fnparse - http://github.com/joshua-choi/fnparse * Java: jparsec - http://jparsec.codehaus.org/ [edits: formating]
- jasonkester 16y ago
  I think this actually illustrates the other guy's point. If you want a parser, you need to go download code off the internet. If you want a Regex, you type something along the lines of new Regex().
  - util 16y ago
    http://research.microsoft.com/en-us/um/people/daan/parsec.html http://research.microsoft.com/en-us/um/people/daan/parsec.ht... "Nowadays, Parsec is distributed with the standard Haskell libraries with most Haskell compilers (GHC, NHC, Hugs)."
- trevorcreech 16y ago
  Treetop for Ruby looks pretty cool too: http://treetop.rubyforge.org/ http://treetop.rubyforge.org/

by brehaut 16y ago

philwelch 16y ago

Your link advocates writing parsers in situations where regexes aren't powerful enough, which is quite sensible and even quite practical in some cases. But there's a big reason regexes are overused compared to parsers--regex engines come stock in most programming languages, and parser generators don't. There's a big mismatch in complexity between overusing something the language gives you for free and building in a parser. Perl 6 deserves some credit for their "rules" system, which can actually take a grammar and parse from it.

brehaut 16y ago
Agreed, the impedance of parsers has traditionally been much higher than for regexps. However, a lot of languages now have some sort of parse combinator library which dramatically increases the ease of writing a parser. I'm thinking specifically of the Parsec inspired family, which has implementations or derivations in many common languages, even C# and Java (despite being noticably more cumbersome in those cases there). [I cannot speak for perl 6, but i trust you are correct]

brehaut 16y ago

Seeing how im advocating that everyone should know when to be using parsing tools rather than cobbling together a regexp cludge, here are some links to some relevant tools in a variety of languages. Note that these are not parser generator tools, but parser combinator libraries: * Python: PyParsing - http://pyparsing.wikispaces.com/ - this is probably the most well respected parser library for python picoparse - http://github.com/brehaut/picoparse - My parsec inspired parser combinator library. It is significantly more light weight than pyparsing, and I would recommend pyparsing in its place for more heavy lifting parsers. * Ruby: RParsec - http://rubyforge.org/projects/rparsec/ - A ruby implementation of Parsec. I've heard good things about it. * Haskell: Parsec - http://legacy.cs.uu.nl/daan/parsec.html - This is an amazing library, worth anyones time. http://book.realworldhaskell.org/read/using-parsec.html http://www.haskell.org/haskellwiki/Parsec * F#: FParsec - http://www.quanttec.com/fparsec/ - This is reason enough to learn F#; it is a fairly true port of the haskell library and very nice to use. * Scala: Packrat Parsing - I believe this is part of the standard lib. http://www.scala-lang.org/docu/files/api/scala/util/parsing/combinator/PackratParsers.html * Clojure: fnparse - http://github.com/joshua-choi/fnparse * Java: jparsec - http://jparsec.codehaus.org/ [edits: formating]

jasonkester 16y ago
I think this actually illustrates the other guy's point. If you want a parser, you need to go download code off the internet. If you want a Regex, you type something along the lines of new Regex().
- util 16y ago
  http://research.microsoft.com/en-us/um/people/daan/parsec.html http://research.microsoft.com/en-us/um/people/daan/parsec.ht... "Nowadays, Parsec is distributed with the standard Haskell libraries with most Haskell compilers (GHC, NHC, Hugs)."
trevorcreech 16y ago
Treetop for Ruby looks pretty cool too: http://treetop.rubyforge.org/ http://treetop.rubyforge.org/