David Woolley [david@djwhome.demon.co.uk] wrote:
> Meta syntaxes for programming languages are almost as old as programming
> languages, e.g. Backus Naur Form.

This isn't quite what Aaron is describing though; Backus Naur Form will not result in a document which, upon a machine's reading it, means the machine can now parse and execute code written in the language described.

This *is* true of XML DTDs - if I provide a machine capable of understanding XML a DTD and XML, it immediately knows what to do with that XML.

I think this is what Aaron is asking for - metadata with constructs like

if_begin ::= if
if_test  ::= ( condition )

etc. If this language were "PDTD," then a program written in Python and a PDTD for Python are all that would be needed for a PDTD-capable machine. This could have very beneficial results; if .Net supported "PDTD," then all I would need to do is write a PDTD for SmallTalk and I can suddenly write SmallTalk programs for my .Net applications.

The question is worthwhile. But as I said earlier, this is not the mailing list for the question.

-Chris "SoopahMan" Moschini
http://hiveminds.info/ 
http://soopahman.com/