Hi,
Last days I have been thinking about scripting support. With my last
patch it should be easy to implement. I hope Vladimir is still
interested in this.
The most important is the general design. I think we shouldn't put
too much in the core and not even in normal mode. This is the same
approach bash has taken. I think the core functionality should be:
- variables (we have that)
- functions
Functions should work *exactly* like normal GRUB commands. In
that case we can easily mix GRUB commands and functions.
- Return values
All commands should be able to return a value. That's also what
bash has. This value can be stored in a variable or simply
returned, I am not too sure about that. Just check what bash
does.
- Conditional statements like if and case
- loops: until, while and for
Whenever a command line should be executed or when a script file is
executed, it's the same. The block of code is just parsed and
executed by a function (the parser, I guess :)).
It's important to see that GRUB does not do anything like
calculations. All this can be moved into a command. When making a
bash script you have the same, there is the expr command. So we have
to keep the core functionality minimal and should offer the commands
in command/ like we do now.
First the lexer. I think it should work like this:
normal/parser.c should contain the lexer. The prototypes etc. can
just be added to include/grub/parser.h.
There are just a few tokens we have to recognize. Think about stuff
like a string of text, if, elif, case, ;, [], etc.
The parser can be quite simple. It has to support all kinds of loops,
etc. I am not sure how to deal with that. perhaps we have to feed
the block within a for loop (for example) to the parser until the for
loop exits. Another possibility is creating some kind of P-code and
parse that later on. I wonder what the best approach is.
For the parser we should use bison, I think. Writing a handwritten
parser is acceptable if some standard approach is taken and it's
really really clean and well documented.
Any idea is welcome. I hope we can discuss the implementation in
detail so we can have scripting support soon.
Thanks,
Marco
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