Adding new commands to ZX BASIC

[boriel]

Ok, well I'll code the commands up as libraries, but I'd still like to know how to add commands.

If by 'commands' you mean something like:
<identifier> <expression>, <expression> ...
E.g.
SCROLL 20, a, 30, c
No, it can't be done.
A library is just a .bas file with subroutines and functions (see for example point.bas or attr.bas). It's just that, nothing else.
Otherwise, yes, we have to touch the parser and at the moment this is not that easy.