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Validating a Credit Card Number

Problem

You want to to preliminary validation of a credit card number, such as for detecting typographical errors in user input.

Solution

Use the ccnum.scm library (available from http://www.neilvandyke.org/ccnum-scm/), which can be loaded as:

(require (lib "ccnum.ss" "ccnum"))

To validate on the check digit, the detected issuer, and the digit count expected of that issuer's numbers:

> (credit-card-number-seems-ok? "4408 0412 3456 7893")
#t

To only test the check digit:

> (credit-card-number-check-digit-ok? "5551 2121 9")
#t
> (credit-card-number-seems-ok?       "5551 2121 9")
#f

A little more information is available with:

> (check-credit-card-number "5551 2121 9")      
(#f 9 mastercard)

The ccnum.scm library also has support for formatting credit card numbers.

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Contributors

-- NeilVanDyke - 16 May 2004