On Wed, 13 Apr 2011 22:41:23 +0100
Peter Clifton <pcjc2@xxxxxxxxx> wrote:
> On Wed, 2011-04-13 at 22:26 +0100, Peter Clifton wrote:
>
> > pin[pinnumber=1] {
> > pinnumber="99";
> > }
>
> And regarding stuff like the above - where we key off one attribute
> and change it in the rule, IF that is ever legal - we should do it
> like a PLC executes its processing cycles.
>
> Freeze a view of the attributes as exist "before", run the rules on
> those frozen attributes, then bulk update. That would enable a
> pin-swap with syntax such as:
>
> pin[pinnumber=1] {pinnumber="2";}
> pin[pinnumber=2] {pinnumber="1";}
It might make things simpler and more uniform for both the program and
for the user if we had different operators for equality testing and for
assignment. Something like one of the following:
Equality test Assignment Comment
x = y x := y Ada, ALGOL, Dylan, Eiffel, Pascal
x = y x <- y R, Objective Caml
x == y x = y C, C++, Java, C#, Python
Even though I am most accustomed to C/C++/Java style, I think that it
is ideal to use â=â in the mathematical sense of a logical statement
with a truth value, using another operator to make assignments more
obvious.
Regards,
Colin
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