valtype::verhoeff(3) Validation for plain number with a VERHOEFF checkdigit


package require Tcl 8.5

package require snit 2

package require valtype::common

package require valtype::verhoeff ?1?

valtype::verhoeff validate value

valtype::verhoeff checkdigit value


This package implements a snit validation type for a plain number with a VERHOEFF checkdigit.

A validation type is an object that can be used to validate Tcl values of a particular kind. For example, snit::integer, a validation type defined by the snit package is used to validate that a Tcl value is an integer.

Every validation type has a validate method which is used to do the validation. This method must take a single argument, the value to be validated; further, it must do nothing if the value is valid, but throw an error if the value is invalid:

    valtype::verhoeff validate .... ;# Does nothing
    valtype::verhoeff validate .... ;# Throws an error (bad verhoeff checkdigit).

The validate method will always return the validated value on success, and throw the -errorcode INVALID on error, possibly with additional elements which provide more details about the problem.


The API provided by this package satisfies the specification of snit validation types found in the documentation of Snit's Not Incr Tcl.
valtype::verhoeff validate value
This method validates the value and returns it, possibly in a canonical form, if it passes. If the value does not pass the validation an error is thrown.
valtype::verhoeff checkdigit value
This method computes a check digit for the value. Before doing so it is validated, except for a checkdigit. If the value does not pass the validation no check digit is calculated and an error is thrown instead.


As said in the package description, the errors thrown by the commands of this package in response to input validation failures use the -errorcode INVALID to distinguish themselves from package internal errors.

To provide more detailed information about why the validation failed the -errorCode goes actually beyond that. First, it will contain a code detailing the type itself. Here this is VERHOEFF. This is then followed by values detailing the reason for the failure. The full set of -errorCodes which can be thrown by this package are:

The input value contained one or more bad characters, i.e. characters which must not occur in the input for it to be a plain number with a VERHOEFF checkdigit.
The check digit of the input value is wrong. This usually signals a data-entry error, with digits transposed, forgotten, etc. Of course, th input may be an outright fake too.


This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category valtype of the Tcllib Trackers []. Please also report any ideas for enhancements you may have for either package and/or documentation.


Checking, Testing, Type checking, Validation, Value checking, isA, verhoeff


Validation, Type checking


Copyright (c) 2011 Andreas Kupries <[email protected]>