RegExpBuilder – Create regular expressions using chained methods

Post by jerf » Wed, Feb 11, 2015, 5:59 PM UTC

DenisM wrote: post #13

marktangotango wrote: post #6

Generally, I find that if one's regexes are so complex that one needs visualizers or other aids in writing them, one doesn't have a regex problem, but a parsing problem. The method of parsing by recursive descent can often lead to much more understandable (if more verbose) "pattern matching".

Recursive descend is imperative, while regex is declarative. Regex may be ugly, but you lose something important when you move from declarative to imperative.

Post by GhotiFish » Wed, Feb 11, 2015, 6:05 PM UTC

_lce0 wrote: post #14

chris-at wrote: post #2

Thanks, this is a lot better than writing this (even if the formatting worked here): ``` (?xi) \b ( # Capture 1: entire matched URL (?: [a-z][\w-]+: # URL protocol and colon (?: /{1,3} # 1-3 slashes | # or [a-z0-9%] # Single letter or digit or '%' # (Trying not to match e.g. "URI::Escape") ) | # or www\d{0,3}[.] # "www.", "www1.", "www2." … "www999." | # or [a-z0-9.\-]+[.][a-z]{2,4}/ # looks like domain name followed…

actually most of the comments seem to imply that whoever wrote that don't fully understand regexp syntax -- or, worst, she expects that whoever read will not /{1,3} # 1-3 slashes | # or [a-z0-9%] # Single letter or digit or "%";

Post by draegtun » Wed, Feb 11, 2015, 6:21 PM UTC

    digits: digit: charset "0123456789"

    rule: [
        thru "$"
        some digits
        "."
        digit
        digit
    ]

    parse "$10.00" rule    ;; true


    pattern: [
        some "p"
        2 "q" any "q"
    ]

    new-rule: [
        2 pattern
    ]

    parse "pqqpqq" new-rule    ;; true

Post by d4n3 » Wed, Feb 11, 2015, 7:06 PM UTC

UnoriginalGuy wrote: post #16

UK-AL wrote: post #12

Earlier quoted context omitted.

Regular expressions are high performance if you use automata style(Regular Language) regular expressions, which limits the use of some of the features you can use. Modern regular expression engines in a lot of languages, actually go beyond the expressiveness of a regular language. This is what damages performance. There is no reason why this would reduce performance... if its not doing anything crazy. If anything you…

I guess it depends on your definition of "high performance." If a regular expression runs too often, even pre-compiled (as they should be), you'll want to replace them with code written in the native language. I've gone in and replaced a one line search/replace written in RegX (compiled), with just a C-style for() loop over the wchar array, and had the memory usage drop by near 80% and performance increase by over 60…

Post by UnoriginalGuy » Wed, Feb 11, 2015, 7:13 PM UTC

d4n3 wrote: post #28

UnoriginalGuy wrote: post #16

Earlier quoted context omitted.

I guess it depends on your definition of "high performance." If a regular expression runs too often, even pre-compiled (as they should be), you'll want to replace them with code written in the native language. I've gone in and replaced a one line search/replace written in RegX (compiled), with just a C-style for() loop over the wchar array, and had the memory usage drop by near 80% and performance increase by over 60…

> you'll want to replace them with code written in the native language Probably not true for Javascript (and other scripted languages) - matching regex uses native and highly optimized regex lib, which will usually be orders of magnitude faster than implementing this in the language.