RAPL is an acronym for Rapid Application Programming Language.
Right now it is Tcl Parser in Javascript (similar to the parser in incr Tcl in Javascript), which produces a binary struct like meta representation of the parsed input. Maybe in the future there will be some extensions to standard Tcl. It will not support all of Tcl, it will support that part of Tcl, which can be run in a browser environment.
The meta information is built using ArrayBuffer and DataView (typed arrays )
It is a work in progress started at November 2011.
The idea is to have some code (in whatever language C/Javascript/others) which can do optimisation on that meta representation and then have a backend (again in whatever language C/Javascript/others) to interpret the meta information.
The first first version will be: also the backedn (interpreter) will be in Javascript and it is planned to use that eventually as a general possibility to run RAPL/Tcl input in a browser and on smart phones.
Stay tuned!