[fpc-pascal] Array assignment, and not-a-number
Mark Morgan Lloyd
markMLl.fpc-pascal at telemetry.co.uk
Mon Apr 15 20:17:09 CEST 2013
Jonas Maebe wrote:
> On 15 Apr 2013, at 16:48, Mark Morgan Lloyd wrote:
>> I was having a bit of fun earlier while waiting for a call. Am I correct in believing that something like
>> type t1= array of integer;
>> var a1: t1;
>> x: integer;
>> a1 := [1,2,3,4,5];
>> can't be done at present, irrespective of any custom definition of the := operator?
> Maybe if you overload the assignment operator for "t2=set of byte" to "t1" assignments, but I'm not certain. It's definitely not something we explicitly support.
That's a good point, although obviously ordering would be lost. After
I'd tinkered with it for a while I concluded that it was probably
related to the discussion of tuples a few weeks ago.
>> Is there an accessible not-a-number constant, to allow me to do something like
>> var reduce: double= NAN;
>> x := reduce + a1;
>> with an appropriate definition of the + operator without risk that an error would try to evaluate it as an ordinary arithmetic expression?
> We don't have constant to identify a qNaN. I don't even know whether all architectures support them. Currently, the only way to achieve the above is by masking exceptions for invalid floating point operations: math.SetExceptionMask(math.GetExceptionMask + [exInvalidOp]).
Thanks, noted. In practical terms the value isn't important, and I could
obviously use something like a null variant or for that matter a nil
pointer as a marker.
> You cannot overload/override operators that have a built-in meaning in the language (such as double+double).
Understood, but what I'm doing here is using "reduce +" as an
experimental alternative to APL's +/ or Vector Pascal's \+ to reduce the
dimension of the right operand by applying the operator:
7 9 11 13 5
I've not investigated SSE or spreading over multiple cores yet, and
probably won't due to time issues. My only incentive was looking for
some alternative to Vector Pascal's higher-level functions, since
obviously something like \<operator> <array> couldn't be achieved
without major compiler surgery.
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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