I Love Tcl

So, I have been grinding through a lot of GUI code (NewStars update coming soon!)...

In the process, I have been shifting code from C++ to direct XML access. Part of this involves something called "XPath" (which I had never heard of before).

The key is, you can query an XML document like a database (including wildcard and logical test patterns). So, if I want the node with the planet with object id stored in variable 'pid', I can do:

set n [$nsGui::turnRoot selectNodes //PLANET_LIST/PLANET\[OBJECTID=$pid\]]

'//' means a relative search (not necessarily from the root). I need "PLANET_LIST" because there is another list of planets, called "UNIVERSE_PLANET_LIST". The outer square bracked "[]" are part of Tcl (execute this part, and resolve it to the string that is returned). The inner (escaped) brackets are part of XPath (return nodes which satisfy "[logical_condition]").

Of course, any language can support XPath. But, in Tcl, I can open a console session, source the stars.tcl, and start issuing XPath commands against the turn file. That allows me to rapidly tune my request to get the results I want (eliminating the compile/re-run steps). Especially since the W3C XPath docs are unreadable...

Then, once I have the planet node, I can pick off attributes:
set concs [$n selectNodes string(MINERALCONCENTRATIONS/text())]

That replaces:
set planXML [xml2list [newStars $::ns_planet $id $::ns_getXML]]
set mainXML [lindex $planXML 2]
set cargoXML [findXMLbyTag "CARGOMANIFEST" $mainXML 2]
set tuple [lindex $cargoXML 1]

Especially since that used "xml2list", which can't always parse some XML...