[fpc-pascal] Array assignment, and not-a-number

[Mark Morgan Lloyd]

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:

c1:
7 9 11 13 5
+/ c1:
45

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

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