Re: Parsing nested parentheses

This is probably a klunky solution, but it reminded me of a parser I had written.. (Evaluate Expressions.)

Quickly hacking at it and only testing a few simple cases (you've been warned)

You could use the returned structure to search for whatever criteria you desire. I'm sure someone here has a much more elegant solution, but my regex abilities are rather limited...

#!/usr/bin/perl

use warnings;
use strict;
use Data::Dumper;
my $input = '(a,b,(c,d,(e,f,g)))';

print Dumper parse_expression($input);

sub parse_expression {
    my $exp = shift;
    my @tokens = ();
    $exp=~s/\s*([()])\s*/ $1 /go;
    # Get tokens
    push @tokens, $1 while $exp=~/\G\s*(".*?")/gc or $exp=~/\G\s*('.*?
+')/gc or $exp=~/\G\s*(\S+)/gc;
    
    # Find any parens. 
    my (@lp,@rp) = ();
    for (my $p =0; $p < @tokens; $p++){
        if ($tokens[$p] eq '('){
            push @lp,$p;
        }elsif($tokens[$p] eq ')'){
            push @rp,$p;
        }
    }
    
    if ( @lp != @rp){
        warn "Mismatched parens in expression.\n";
        return;

    }

    my @temp = @tokens;
    for (my $i=0; $i < @rp; $i++){
         my @wanted;
         for (my $j = $#lp; $j >= 0 ; $j--){
            if ( defined $lp[$j] && $lp[$j] < $rp[$i] ){
                (undef,@wanted) = @tokens[ $lp[$j] ..  ($rp[$i] - 1 ) 
+] ;    
                @tokens[ $lp[$j] ..  ($rp[$i]) ] = [ grep {defined $_ 
+} @wanted];
                push @temp, map {split /\s*,\s*/} @wanted;
                $lp[$j] = $rp[$i] = undef;
                last;
            }
         }
    }

  return $tokens[0];

}

__DATA__
# OUTPUT
$VAR1 = 
          [
            'a,b,',
            [
              'c,d,',
              [
                'e,f,g'
              ]
            ]
          ];
[download]

-Lee

"To be civilized is to deny one's nature."

Comment on Re: Parsing nested parentheses Download Code

Replies are listed 'Best First'.
Re^2: Parsing nested parentheses by bassfox (Initiate) on Jun 19, 2008 at 08:20 UTC
Hi there, ever thought of using the perl internal functions to import a nested data structure to a LoL? If you do not have to avoid using eval, you could do it real simple like this: `#!/usr/bin/perl -w use strict; use Data::Dumper; my $string = "(a,b,(c,d,(e,f,g)))"; $string =~ s/([^,\(\)]+)/"$1"/gsm; # quote content $string =~ tr/\(\)/\[\]/; # replace braces my @LoL; # define list eval("\@LoL = $test;"); # fill LoL print Dumper @LoL; __DATA__ Output: $VAR1 = [ 'a', 'b', [ 'c', 'd', [ 'e', 'f', 'g' ] ] ];` [download] It is not extensively tested, but should work for most items. - frank	[reply] [d/l]

Replies are listed 'Best First'.

Re^2: Parsing nested parentheses
by bassfox (Initiate) on Jun 19, 2008 at 08:20 UTC

#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my $string = "(a,b,(c,d,(e,f,g)))";
$string =~ s/([^,\(\)]+)/"$1"/gsm;    # quote content
$string =~ tr/\(\)/\[\]/;             # replace braces

my @LoL;                              # define list
eval("\@LoL = $test;");               # fill LoL

print Dumper @LoL;

__DATA__

Output:
$VAR1 = [
          'a',
          'b',
          [
            'c',
            'd',
            [
              'e',
              'f',
              'g'
            ]
          ]
        ];
[download]

[reply]
[d/l]