An initial prototype of the Rivet's FormBroker is now available from


The code is inspired by Karl's original code but it goes further ahead trying to become a form definition repository. The overall style of the package has an OOP flavor even though no one of the OOP environments available for Tcl was used. It's just 'namespace ensemble' based. I will henceforth use the word 'object' meaning any instance of form descriptor created by the FormBroker package.

Forms definition objects are referenced through commands generated by the FormBroker package with the 'create' call

set fbobj [::FormBroker create \
                        {var1 string bounds 10 constrain quote} \
                        {var2 email} \
                        {var3 integer bounds 10} \
                        {var4 unsigned bounds {10 100} constrain}]

which is quite similar to the original form broker: each element in the argument list is a list in its own right in which the first and second element must be the form variable name and type. At the moment supported types are 'string', 'integer', 'unsigned', 'email'. Each of them has its own validation procedure. The supported variable types can be extended easily, but non portably: I mean that writing a validator requires explicit manipulation of the dictionary that provides a form variable internal representation. (As such it's a design flaw, at the moment). The keyword 'constrain' means that, when possible, a value is brought within its assigned bounds. For a 'string' it means the string has to be truncated to be n characters when longer.

The namespace ensemble offers also a 'creategc' method that demands a Tcl variable name as first argument. The command name is returned and also stored in the named Tcl variable. When this Tcl variable is destroyed the unset trace that ensues triggers the object destructor to be called, causing the form internal representation to be garbage collected...

 A form response is then checked calling

 $fbobj validate response

where 'response' is the usual array of variables made by ::rivet::load_response. This method returns 'true' if the array validates. If the validation fails the method

$fbobj failing

returns a list of variable names with the validation error codes.

Variables can be quoted and the quoting function can be customized (the internal function just puts a variable value between single quotes). A custom function for quoting must have the very basic form

set quoted_string [<quoting-proc> $orig_string]

the need for quotation can be variable specific (in that case 'validate' quotes in the 'response' array only the variables eligible to be quoted). Overall quoting can be forced by calling

$fbobj validate -forcequote response

There is more to say but I don't want to bother you any further. I will answer your questions with pleasure. The namespace ensemble API is open to be amended if you have some strong idea on how to redesign it. I won't set out writing the documentation any soon: I'm going to allow more time to see if the design settle down using the package in regular development (which I still have to do!). If you're interested to write a specific data type validator I will show you how to (there's an example in trunk/contrib/validate_mac.tcl which shows how to validate a mac address)

 -- Massimo

P.S. I will certainly remove the 'namespace export *' line from the package in order to keep private all the methods not intended for application level programming

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