$programSource =~ s/in \(
    (' <-- outer group start goes in $1
      ([^']*)  <-- inner group chars between ''
             '[,])*  <-- followed by optional comma, close outer group and repeat outer group for any number of repetitions
                   \)/=~ m#[$2$3$4$5$6$7$8$9]#;/g;  <-- put inner groups in match (up to 8 of them, anyway)