my @result =
   map
   {
       local our $res;
       m
       {(?x)
          ^
          (?(?=([a-z])$)
             (?{ $res = qq{$1=>fn($1)}; })
             |
             (?(?=([a-z])=([a-z])$)
                (?{ $res = qq{$2=>$3}; })
                |
                (?(?=([a-z])=\#([a-z])$)
                   (?{ $res = qq{$4=>fn($5)}; })
                   |
                   (?{ $res = q{???}; })
                )
             )
          )
       };
       $res
   }
   split m{,}, $str;

##</code><code>##

my @result =
   map
   {
       (/([a-z])$/
          ? qq{$1=>fn($2)}
          : (/([a-z])=([a-z])$/
               ? qq{$1=>$2}
               : (/([a-z])=\#([a-z])$/
                    ? qq{$1=>fn($2)}
                    : q{???}
                 )
            )
       )
   }
   split m{,}, $str;