my @result = $prBoundaryString =~ m{$coord}g;
# check if scalar (@result / 2) % 2 == 1

# or

my $count = 0;
while ($prBoundaryString =~ m{$coord}g) {
    my ($x, $y) = ($1, $2);
    $count++;
}
[download]

The example I posted is simplified - perhaps too much.

I really want repetition, not recursion, but ran into roadblock with perl behaviour of only returning the last matches. Here is what I first tried, it only returns the last coordinate pair, which is documented behaviour.

#!/usr/bin/env perl

use v5.16;
use strict;


my $prBoundaryString = <<endPrBoundary;
'( (0.01 0.02) (0.0 1328.23) (0.03 0.04) )
endPrBoundary

say "prBoundaryString=$prBoundaryString";

   my ($coord,$coords);

   $coord = qr{
      \(\s*
         (?<x>[\-\.0-9]+)\s+ 
         (?<y>[\-\.0-9]+)\s*
      \)\s*
   }x;

   $coords = qr{
   (
      ( $coord )+
   )
   }x;

   $prBoundaryString =~ m{
       \'\(\s*\s*
       $coords
       \)\s*$
   }x || die "parsePrBoundary: Error parsing prBoundary";

   say "-x0=$-{x}[0]";
   say "-y0=$-{y}[0]";
   say "-x1=$-{x}[1]";
   say "-y1=$-{y}[1]";
   say "-x2=$-{x}[2]";
   say "-y2=$-{y}[2]";
[download]

output: - it only gets the last coordinate.

prBoundaryString='( (0.01 0.02) (0.0 1328.23) (0.03 0.04) )

-x0=0.03
-y0=0.04
-x1=
-y1=
-x2=
-y2=
[download]

darisler,
If you use a regex with the global modifier in scalar context, you will get an iterator allowing you to go through each set of matches one at a time (like one of the examples above):

while ($str =~ m{$your_regex}g) {
    my ($x, $y) = ($1, $2);
    # This loop will repeat for as many matches as are in $str
}
[download]

Cheers - L~R

Hi darisler,
Trying to write some code that reads in a list of coordinates, must have an odd number for some odd reason... but I'd like to know how to define '$coords' recursively

Do you have to define '$coords' recursively or repeatedly? And I don't know why you are using your regex like you are doing. If I get what you wanted, you can simply use split to get all the coords into an array, so they are in right order as follow in your original string, then loop for this like so:

use v5.16;
use strict;

my $prBoundaryString = <<endPrBoundary;
'( (0.01 0.02) (0.0 1328.23) (0.01 0.02) (0.04 0.53) (0.03 44.23)
   (0.0 1328.23) (0.04 0.53)
 )
endPrBoundary

say "prBoundaryString=$prBoundaryString";

my @pts = grep { /\d+/ } split /\s+|[()]/, $prBoundaryString;

my $count = 0;
for ( 0 .. $#pts ) {
    if   ( $_ % 2 == 0 ) { print qq[-x$count=$pts[$_]] }
    else                 { print qq[-y$count=$pts[$_]]; $count++ }
}
[download]

prBoundaryString='( (0.01 0.02) (0.0 1328.23) (0.01 0.02) (0.04 0.53) 
+(0.03 44.23)
   (0.0 1328.23) (0.04 0.53)
 )

-x0=0.01
-y0=0.02
-x1=0.0
-y1=1328.23
-x2=0.01
-y2=0.02
-x3=0.04
-y3=0.53
-x4=0.03
-y4=44.23
-x5=0.0
-y5=1328.23
-x6=0.04
-y6=0.53
[download]