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# valtype::isbn(n) 1 tcllib "Validation types"

## Name

valtype::isbn - Validation for ISBN

## Synopsis

- package require Tcl 8.5
- package require snit 2
- package require valtype::common
- package require valtype::isbn ?1?

- valtype::isbn validate value
- valtype::isbn checkdigit value
- valtype::isbn 13of value

## Description

This package implements a snit validation type for an ISBN.

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::isbn validate .... ;# Does nothing
        valtype::isbn validate .... ;# Throws an error (bad ISBN).

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.

## API

The API provided by this package satisfies the specification of snit validation types found in the documentation of Snit's Not Incr Tcl.

valtype::isbn 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::isbn 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.

valtype::isbn 13of value

  This method expects an old-style 10-digit ISBN and returns the canonical modern 13-digit ISBN. This is used by validate to canonicalize the input, so that all parts of the system after the validation can expect to work with modern 13-digit ISBNs.

## Error Codes

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 ISBN. 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:

INVALID ISBN CHARACTER

  The input value contained one or more bad characters, i.e. characters which must not occur in the input for it to be an ISBN.

INVALID ISBN CHECK-DIGIT

  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.

INVALID ISBN LENGTH

  The input value is of the wrong length to be an ISBN.

## Bugs, Ideas, Feedback

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.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

## Keywords

Book Number, Checking, EAN, EAN13, European Article Number, ISBN, International Article Number, International Standard Book Number, Testing, Type checking, Validation, Value checking, isA

## Category

Validation, Type checking

## Copyright

Copyright © 2011 Andreas Kupries <andreas_kupries@users.sourceforge.net>