In my application, I allow qr// and ' and ", but not others like qq//, qx//, s/// or tr///. In qr//, I scan for any use of (?{...}) and fail for those. I just bring it up to show that you can choose your rules pretty flexibly.

(Expanded answer.)

As for "how to use the code blocks in a production," just realize that there's no real difference between the parsing parts and the code parts: if you get through all of the subrules in the production, then the whole production succeeds and passes whatever is in $return up to the calling rule. The code blocks in YACC are very distinct, but code blocks in P::RD are more like embedded (?{}) code in a regexp. (That was my revelation thanks to another monk a few weeks ago.)

So, do whatever you want in a code block. The items so far are in @item and %item. You can assign whatever you want to assign into $return, including undef to fail the rule.

string:    <perl_quotelike>
    { if ($item[1][0] =~ /^(qx|s|tr|y)$/ or  # no perl commands
          $item[1][1] eq '`' or              # no backticks
          $item[1][2] =~ /\(\?\??\{/)        # no qr'' with code
      { $return = undef }
      else
      { $return = eval "" . join('', @{$item[1]}) }
      (defined $return)
    }
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