Re: [PATCH v2] dtc: Add support for named integer constants

Hi Grant,

On Thu, Sep 8, 2011 at 11:32 AM, Grant Likely [off-list ref] wrote:

On Thu, Sep 08, 2011 at 06:09:27AM -0700, Simon Glass wrote:

quoted

Hi Stephen,

On Fri, Sep 2, 2011 at 11:34 AM, Stephen Warren [off-list ref] wrote:

quoted

Stephen Warren wrote at Tuesday, August 30, 2011 3:30 PM:

quoted

You may define constants as follows:

/define/ TWO 2;
/define/ FOUR 4;
/define/ OTHER FOUR;

And properties may use these values as follows:

foo = <1 TWO 3 FOUR 5>;

Signed-off-by: Stephen Warren <redacted>

David, Jon,

Does this seem reasonable?

I think the syntax is simple enough it wouldn't interfere with any more
advanced expression/function/... support in the future, and it could be
easily extended to allow e.g.:

/define/ FOO "BAR";
/define/ BAX [0af8dacb0];
...

This seems very reasonable to me, and very useful. From the syntax it
looks like lower case symbols are allowed also, which is fine with me.

I hope that this can go into dtc as we would definitely use it.

What are the risks of symbol conflict with this approach?  I'm
concerned that a poorly chosen /define/ name will break parsing in
non-obvious ways.  Would it be better to have a every define reference
to be explicit in the syntax?

Can you give an example of symbol conflict?

I vote against explicit syntax...things like $var are pretty ugly I
think. We will end up with Perl. Let's make these defines first class
citizens.

It should be clear enough since these will appear within a value -
i.e. I assume we will do:

/define/ ONE 1
...
/ {
   testing = <ONE TWO THREE>;
}

but not:

/define/ which testing
/ {
   which = <1 2 3>;
}

which does seem a little ambiguous (although not unresolveable by the
parser with the help of the symbol table).

Regards,
Simon

g.