StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>Matching parens with a regex is quite possible.</p> <p>Here is a Perl script that will parse arbitrary deep matching parens. While it will throw out the non-matching parens outside, I did not design it specifically to validate parens. It will parse arbitrarily deep parens so long as they are balanced. This will get you started however.</p> <p>The key is recursion both in the regex and the use of it. Play with it, and I am sure that you can get this to also flag non matching prens. I think if you capture what this regex throws away and count parens (ie test for odd parens in the non-match text), you have invalid, unbalanced parens. </p> <pre><code>#!/usr/bin/perl $re = qr / ( # start capture buffer 1 \( # match an opening paren ( # capture buffer 2 (?: # match one of: (?> # don't backtrack over the inside of this group [^()]+ # one or more ) # end non backtracking group | # ... or ... (?1) # recurse to opening 1 and try it again )* # 0 or more times. ) # end of buffer 2 \) # match a closing paren ) # end capture buffer one /x; sub strip { my ($str) = @_; while ($str=~/$re/g) { $match=$1; $striped=$2; print "$match\n"; strip($striped) if $striped=~/\(/; return $striped; } } while(<DATA>) { print "start pattern: $_"; while (/$re/g) { strip($1) ; } } __DATA__ "(apple + (-0.5)) * (boy - 1)" "((((one)two)three)four)x(one(two(three(four))))" "a) * (b + c) / (d" "-a * (b / 1.50)" </code></pre> <p>Output:</p> <pre><code>start pattern: "(apple + (-0.5)) * (boy - 1)" (apple + (-0.5)) (-0.5) (boy - 1) start pattern: "((((one)two)three)four)x(one(two(three(four))))" ((((one)two)three)four) (((one)two)three) ((one)two) (one) (one(two(three(four)))) (two(three(four))) (three(four)) (four) start pattern: "a) * (b + c) / (d" (b + c) start pattern: "-a * (b / 1.50)" (b / 1.50) </code></pre>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload