[fpc-devel] XML node dump feature

[J. Gareth Moreton]

Sorry for the mistake in "RoughExp" - the first line is supposed to be 
"Result := 1 + X;", not "Result := Exponent;".

On 25/06/2019 06:58, J. Gareth Moreton wrote:
>
> No-one said this would be an easy feature to implement.  This might be 
> a step-by-step process, starting with simple function calls and 
> building up to complex constant assignment. Nevertheless, at least 
> initially, I would prefer to avoid the creation of a pure function 
> that deals with a pointer in any way, including objects, since their 
> values or successful creation (e.g. out of memory errors or the 
> calling of "Fail") cannot be determined at design time.
>
> Still, looking at your example, there's nothing to say that those 
> record methods cannot be made pure, since the records already exist by 
> the time they're called.  If anything, that looks like a relatively 
> good use case to go on.
>
> My initial complex use cases (after simple tests) will be the following:
>
> *function *Factorial(N: QWord): QWord; *pure*; *inline*;
> *var*
>   X: Integer;
> *begin*
>   Result := 1;
> *if *N < 2 *then*
>     Exit;
>
> *for *X := 2 *to *N *do*
>     Result := Result * N;
> *end*;
>
> *function *RecursiveFactorial(N: QWord): QWord; *pure*; /{ Cannot be 
> inlined on account of the recursive call, but can be made pure }/
> *begin*
> *if *N < 2 *then*
> *begin*
>     Result := 1;
>     Exit;
> *end*;
>
>   Result := Result * RecursiveFactorial(N - 1);
> *end*;
>
> *function *RoughExp(X: Double): Double; *pure*;
> *var*
>   Count: Integer;
>   WorkingValue: Double;
> *begin*
> /{ Calculate RoughExp(X) as e^X = 1 + X + X^2/2! + X^3/3! + ... + 
> X^8/8! }/
>   Result := Exponent;
>
> *for *Count := 2 *to *8 *do*
> *begin*
>     X := X * Exponent; { Contains "X^Count" }
>     Result := Result + (X / RecursiveFactorial(Count));
> *end*;
> end;
>
> *function *Bad(X: QWord): QWord; *pure*;
> *begin*
>   Result := 0;
> *while *True *do*
> /{ Run forever }/;
> *end*;
>
> *const*
>   Factorial6 = Factorial(6);/{ Should convert the function call into 
> the immediate value 720 }/
>   Factorial21 = Factorial(21); /{ Should return an error due to 
> arithmetic overflow }/
>   BigNumber = BadCount(0); /{ Should return an error upon realising 
> it's in an infinite loop }/
>
>   RFactorial20: Double = 1 / Factorial(20); /{ Typed constant }/
>   SqrtE = RoughExp(0.5); /{ This also tests compiler efficiency by 
> remembering past results of RecursiveFactorial with identical inputs }/
>   ESquared = RoughExp(2); /{ ... as does this one if a non-recursive 
> factorial is used, due to the previous call to RoughExp(0.5) }/
>
> I may ask you guys for more complex examples down the line. This is 
> something I really want to get working!
>
> Gareth aka. Kit
>
> P.S. Just to clarify... we happy with the directive being '*pure*'?
>
>
> On 25/06/2019 06:20, Sven Barth via fpc-devel wrote:
>> Am 25.06.2019 um 06:20 schrieb Marģers . via fpc-devel:
>>>
>>> ----- Reply to message -----
>>> Subject: Re: [fpc-devel] XML node dump feature
>>> Date: otrd., 25 jūn., 03:16
>>> From:  Ben Grasset <operator97 at gmail.com>
>>> To:  FPC developers' list
>>> <fpc-devel at lists.freepascal.org>
>>>
>>>> const
>>>>    A: TVec3F = (X: 1.2; Y: 2.4; Z: 3.8);
>>>>    B: TVec3F = (X: 2.1; Y: 4.2; Z: 8.3);
>>>>    // You can't do the next part currently, obviously
>>>>    C: TVec3F = A + B;
>>>>    D: TVec3F = A - B;
>>>>    E: TVec3F = A * B;
>>>>    F: TVec3F = A / B;
>>>>
>>> Sorry to say but, this should not work even with
>>> *pure* function.  Typed constants are not truly
>>> constants.
>> Correct. Though considering that we're talking about *compile time* 
>> the compiler *could* treat consts (in {$J-} mode) as constants if 
>> pure functions are involved... Though it would need a bit more work 
>> as currently the compiler is "simply" piping the constant values of 
>> typed constants into the output assembly.
>>
>> Regards,
>> Sven
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