Create a fill-in web form that uses a JavaScript implementation of the Luhn formula (Exercise 4.10) to check for typos in credit card numbers. (But don’t use real credit card numbers; homework...

Create a fill-in web form that uses a JavaScript implementation of the Luhn formula (Exercise 4.10) to check for typos in credit card numbers. (But don’t use real credit card numbers; homework exercises don’t tend to be very secure!) (a) Modify the code of Figure 14.15 (Example 14.35) so that it replaces the form with its output, as the CGI and PHP versions of Figures 14.11 and 14.14 do. (b) Modify the CGI and PHP scripts of Figures 14.11 and 14.14 (Examples 14.30 and 14.34) so they appear to append their output to the bottom of the form, as the JavaScript version of Figure 14.15 does. 14.11 Run the following program in Perl:

You may be surprised by the output. Perl 5 allows named subroutines to nest, but does not create closures for them properly. Rewrite the code above to create a reference to an anonymous local subroutine and verify that it does create closures correctly. Add the line use diagnostics; to the beginning of the original version and run it again. Based on the explanation this will give you, speculate as to how nested named subroutines are implemented in Perl 5.