NAME

       valtype::verhoeff - Validation for plain number with a VERHOEFF checkdigit

SYNOPSIS

       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

_________________________________________________________________________________________________

DESCRIPTION

       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.

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::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.

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 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:

       INVALID VERHOEFF CHARACTER
              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.

       INVALID VERHOEFF 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.

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
       [http://core.tcl.tk/tcllib/reportlist].  Please also report any ideas for enhancements you
       may have for either package and/or documentation.

KEYWORDS

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

CATEGORY

       Validation, Type checking

COPYRIGHT

       Copyright (c) 2011 Andreas Kupries <andreas_kupries@users.sourceforge.net>