Forum OpenACS Q&A: Additions to the tcl language

What is the current philosophy / thought on adding fundamental tcl commands to OACS?

I want to add a sub command to the tcl dict command and am wondering if it is something that we would want to add to the OACS core and where. Would it go in a loaded tcl module, in an ...init.procs in acs-tcl, or just where?

The addition is a dict getnull sub command that returns the empty string instead of throwing an error when a "get" of a non-existing key is requested. Here is the suggested addition. I found it at http://wiki.tcl.tk/19948. As can be seen, this slips the getnull into the sub commands of dict and appears and is used as any other native sub command of dict.

proc ::tcl::dict::getnull {dictionary args} {
    if {[exists $dictionary {*}$args]} {
        get $dictionary {*}$args
    }
}
namespace ensemble configure dict -map\
    [dict replace [namespace ensemble configure dict -map]\
                  getnull ::tcl::dict::getnull]

Any thoughts? Thanks,

my personal two cents here: although I can see why one could need such a feature, I would not modify a standard tcl command for this. Chances are that this could get overridden or conflict in future tcl versions.

If this ever should make it to the openacs codebase, I would say it should go into a separate proc e.g. util::dict_get.

What is wrong with a oneliner like this? No procs involved and should do the trick

set value [expr {[dict exists dict noexist] ? [dict get dict noexist] : ""}]

Package developers usually implement changes within a separate package.

This usually precludes modifying an existing proc. Changing behavior on an existing proc may adversely affect another that, for instance in this case, expects an error.

If the changes are applicable to the core, core developers tend to find it and incorporate it directly, or by copying the functionality of the code while improving on it.

FWIW, there are a few practical variations of the Tcl dict paradigm in Q-forms package, mainly regarding looping and converting a batch of name values from/to array, lists, and scalars. Special cases allow limiting the names, or assigning an empty string if a value is not found for named index etc.

cheers,
Ben

The most direct approach to add to acs-core is to post a TIP. This thread is about that:
https://openacs.org/forums/message-view?message_id=3472610

cheers,
Ben