I'd like to revise and extend my submission

challenge-044/dave-jacoby/perl/ch-1a.pl

@@ -0,0 +1,33 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use utf8;
+use feature qw{ postderef say signatures };
+no warnings
+  qw{ experimental::postderef experimental::signatures };
+
+my $vals->@* = ( ' + ', ' - ', '' );
+my $source->@* = ( 1, '', 2, '', 3, '', 4, '', 5, '', 6, '', 7, '', 8, '', 9 );
+
+challenge( $source, $vals, 1 );
+
+sub challenge ( $source, $vals, $index ) {
+
+    # check to see if this is correct
+    if ( $index >= scalar $source->@* ) {
+        my $string = join '', $source->@*;
+        my $result = eval $string;
+        say qq{  $result = $string } if $result == 100;
+        return;
+    }
+
+    # recursively add to the array
+    my $next->@* = map { $_ } $source->@*;
+    for my $v ( $vals->@* ) {
+        $next->[$index] = $v;
+        challenge( $next, $vals, $index + 2 );
+    }
+    return;
+}
+exit;