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Parser Combinators Beat Regexes

(entropicthoughts.com)
120 points mooreds | 1 comments | 09 Apr 25 21:53 UTC | HN request time: 0.001s | source
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arn3n ◴[10 Apr 25 00:34 UTC] No.43639465[source]▶
“In other languages, it would be considered overkill to write a full parser when a simple regex can do the same thing. In Haskell, writing a parser is no big deal. We just do it and move on with our lives.”

I see a long code file filled with comments and long paragraph-level explanations. I think I’d rather just learn and use regex.

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layer8 ◴[10 Apr 25 02:07 UTC] No.43639965[source]▶
Whenever I write a regex, I end up with a comments roughly ten times longer than the regex. That being said, regular expressions are often the right tool for the job (i.e. parsing a regular language, as opposed to a context-free language or whatever), just the syntax becomes unreadable rather quickly. I’m sure you could build a nicer regular-expression syntax in Haskell.
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1. f1shy ◴[10 Apr 25 05:16 UTC] No.43640864[source]▶
Yes. Regex tend to become rather fast write only. One solution is commenting, but is still complex. What I like to do now (in C) is define parts of it. Just a crude example to get the idea:

   // STRing: matches anything inside quotes (single or double)
   #define STR "[\"'](.*)[\"']"
   // NUMber: matches decimal or hexadecimal numbers
   #define NUM "([[:digit:]]x?[[:xdigit:]]*)"
   
   regcomp(&reg_exp, STR NUM , REG_EXTENDED | REG_ICASE);
So at the end I compose the RE with the various parts, which are documented separately.