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From: Chris Smith <space DOT dandy AT icloud DOT com>
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Subject: Re: [geda-user] Using Lua to safely read configuration and layout
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Date: Sun, 08 Feb 2015 12:41:12 +0000
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> On 7 Feb 2015, at 23:38, Lev <leventelist AT gmail DOT com> wrote:
> 
> On Sun, 08 Feb 2015 00:00:23 +0100
> Christian Riggenbach <criggenbach AT magahugu DOT ch> wrote:
> 
>> To state the obvious: yeah, that would be a problem. Either code the
>> unit- system in the core (hard to maintain), use something as trivial
>> as "3*mm + $n 
>> * 10*mil" and define mm end the other units as factors (hard to
>> read). And unit-parsing on an higher level would negate the added
>> benefit of a parser in the first way.
> 
> I wouldn't use ANY scripts in the PCB or sch file. That would make life
> very hard. I'd use <whatever scripting language> to parse the data in a
> file. This is the task to be done, just don't overcomplicate the solution. I
> would be happy if it was Lua, but we could roll our own language and parser.
> 
> If there is something we can do, it doesn't mean we must do it.

I agree that scripts/expressions would have little use and cause problems in general schematics which are modified and saved often, but I can also see that it would be very useful for parametric symbols and reusable sub-circuits. I wouldn't want to limit the parser/interpreter to preclude it - it would be better to define what will and won't be supported by the application.

It might be enough simply to say that schematics/symbols can be as dynamic as you like, but they will be evaluated once when instantiated and will be static from that point on.

Chris