# We need use re 'eval' because we use interpolation and (?{...})
# in the same regexp. Beware of the implications of this directive.
use re 'eval';

our @matches;                 # Don't use a lexical for this.
local *matches;               # Protect our caller's variables.
/
   (?{ [] })                  # Create a stack
   $text
   (?:
      \s
      (\w+)
      (?{ [ @{$^R}, $1 ] })   # Save last match on the stack.
   )+
   (?{ @matches = @{$^R}; })  # Success! Save the result.
/x;

##</code><code>##

sub flatten_list {
   my ($rv, $p) = @_;
   @$rv = ();
   while ($p) {
      unshift @$rv, $p->[1];
      $p = $p->[0];
   }
}

our @matches;
local *matches;
/
   $text
   (?:
      \s
      (\w+)
      (?{ [ $^R, $1 ] })
   )+
   (?{ flatten_list \@matches, $^R })
/x;