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<p>Sorry for the mistake in "RoughExp" - the first line is supposed
to be "Result := 1 + X;", not "Result := Exponent;".<br>
</p>
<div class="moz-cite-prefix">On 25/06/2019 06:58, J. Gareth Moreton
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:bdfb9af7-0aba-ee85-7ba3-41db03228bd7@moreton-family.com">
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<p>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.</p>
<p>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.</p>
<p>My initial complex use cases (after simple tests) will be the
following:</p>
<p><tt><b>function </b>Factorial(N: QWord): QWord; <b>pure</b>;
<b>inline</b>;</tt><tt><br>
</tt><b><tt>var</tt></b><tt><br>
</tt><tt> X: Integer;</tt><tt><br>
</tt><b><tt>begin</tt></b><tt><br>
</tt><tt> Result := 1;</tt><tt><br>
</tt><tt> <b>if </b>N < 2 <b>then</b></tt><tt><br>
</tt><tt> Exit;</tt><tt><br>
</tt><tt><br>
</tt><tt> <b>for </b>X := 2 <b>to </b>N <b>do</b></tt><tt><br>
</tt><tt> Result := Result * N;</tt><tt><br>
</tt><tt><b>end</b>;</tt><tt><br>
</tt><tt><br>
</tt><tt><b>function </b>RecursiveFactorial(N: QWord): QWord; <b>pure</b>;
<i>{ Cannot be inlined on account of the recursive call, but
can be made pure }</i></tt><tt><br>
</tt><b><tt>begin</tt></b><tt><br>
</tt><tt> <b>if </b>N < 2 <b>then</b></tt><tt><br>
</tt><tt> <b>begin</b></tt><tt><br>
</tt><tt> Result := 1;</tt><tt><br>
</tt><tt> Exit;</tt><tt><br>
</tt><tt> <b>end</b>;</tt><tt><br>
</tt><tt><br>
</tt><tt> Result := Result * RecursiveFactorial(N - 1);</tt><tt><br>
</tt><tt><b>end</b>;</tt><tt><br>
</tt><tt><br>
</tt><tt><b>function </b>RoughExp(X: Double): Double; <b>pure</b>;</tt><tt><br>
</tt><b><tt>var</tt></b><tt><br>
</tt><tt> Count: Integer;</tt><tt><br>
</tt><tt> WorkingValue: Double;</tt><tt><br>
</tt><b><tt>begin</tt></b><tt><br>
</tt><tt> <i>{ Calculate RoughExp(X) as e^X = 1 + X + X^2/2! +
X^3/3! + ... + X^8/8! }</i></tt><tt><br>
</tt><tt> Result := Exponent;</tt><tt><br>
</tt><tt><br>
</tt><tt> <b>for </b>Count := 2 <b>to </b>8 <b>do</b></tt><tt><br>
</tt><tt> <b>begin</b></tt><tt><br>
</tt><tt> X := X * Exponent; { Contains "X^Count" }</tt><tt><br>
</tt><tt> Result := Result + (X / RecursiveFactorial(Count));</tt><tt><br>
</tt><tt> <b>end</b>;</tt><tt><br>
</tt><tt>end;</tt><tt><br>
</tt><tt><br>
</tt><tt><b>function </b>Bad(X: QWord): QWord; <b>pure</b>;</tt><tt><br>
</tt><b><tt>begin</tt></b><tt><br>
</tt><tt> Result := 0;</tt><tt><br>
</tt><tt> <b>while </b>True <b>do</b></tt><tt><br>
</tt><tt> <i>{ Run forever }</i>;</tt><tt><br>
</tt><tt><b>end</b>;</tt><tt><br>
</tt><tt><br>
</tt><b><tt>const</tt></b><tt><br>
</tt><tt> Factorial6 = Factorial(6);</tt><tt> <i>{ Should
convert the function call into the immediate value 720 }</i><br>
</tt><tt> Factorial21 = Factorial(21); <i>{ Should return an
error due to arithmetic overflow }</i></tt><tt><br>
</tt><tt> BigNumber = BadCount(0); <i>{ Should return an error
upon realising it's in an infinite loop }</i></tt><tt><br>
</tt><tt><br>
</tt><tt> RFactorial20: Double = 1 / Factorial(20); <i>{ Typed
constant }</i></tt><tt><br>
</tt><tt> SqrtE = RoughExp(0.5); <i>{ This also tests compiler
efficiency by remembering past results of RecursiveFactorial
with identical inputs }</i></tt><tt><br>
</tt><tt> ESquared = RoughExp(2); <i>{ ... as does this one if
a non-recursive factorial is used, due to the previous call
to RoughExp(0.5) }</i></tt><tt><br>
</tt></p>
<p>I may ask you guys for more complex examples down the line.
This is something I really want to get working!</p>
<p>Gareth aka. Kit</p>
<p>P.S. Just to clarify... we happy with the directive being '<b>pure</b>'?<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 25/06/2019 06:20, Sven Barth via
fpc-devel wrote:<br>
</div>
<blockquote type="cite"
cite="mid:5abd8901-63c1-89f4-83e8-6dc60cd5b389@googlemail.com">Am
25.06.2019 um 06:20 schrieb Marģers . via fpc-devel: <br>
<blockquote type="cite"> <br>
----- Reply to message ----- <br>
Subject: Re: [fpc-devel] XML node dump feature <br>
Date: otrd., 25 jūn., 03:16 <br>
From: Ben Grasset <a class="moz-txt-link-rfc2396E"
href="mailto:operator97@gmail.com" moz-do-not-send="true"><operator97@gmail.com></a>
<br>
To: FPC developers' list <br>
<a class="moz-txt-link-rfc2396E"
href="mailto:fpc-devel@lists.freepascal.org"
moz-do-not-send="true"><fpc-devel@lists.freepascal.org></a>
<br>
<br>
<blockquote type="cite">const <br>
A: TVec3F = (X: 1.2; Y: 2.4; Z: 3.8); <br>
B: TVec3F = (X: 2.1; Y: 4.2; Z: 8.3); <br>
// You can't do the next part currently, obviously <br>
C: TVec3F = A + B; <br>
D: TVec3F = A - B; <br>
E: TVec3F = A * B; <br>
F: TVec3F = A / B; <br>
<br>
</blockquote>
Sorry to say but, this should not work even with <br>
*pure* function. Typed constants are not truly <br>
constants. <br>
</blockquote>
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. <br>
<br>
Regards, <br>
Sven <br>
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