<div dir="ltr">I, for one, would love to have a compiler do (a) based on (b), my specification of (c), and the ability to pin particular things...<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Jul 22, 2013 at 4:04 PM, wren ng thornton <span dir="ltr"><<a href="mailto:wren@freegeek.org" target="_blank">wren@freegeek.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">On 7/22/13 9:06 AM, Tom Ellis wrote:<br>
> On Mon, Jul 22, 2013 at 07:52:06PM +1200, Chris Wong wrote:<br>
</div><div class="im">>> A binding is memoized if, ignoring everything after the equals sign,<br>
>> it looks like a constant.<br>
>><br>
>> In other words, these are memoized:<br>
</div>> [...]<br>
<div class="im">>> f = \x -> x + 1<br>
</div>> [...]<br>
<div class="im">>> and these are not:<br>
>><br>
>> f x = x + 1<br>
><br>
</div><div class="im">> In what sense is the former memoised? I'm not aware of any difference<br>
> between these two definitions.<br>
<br>
</div>Consider rather,<br>
<br>
f1 = let y = blah blah in \x -> x + y<br>
<br>
f2 x = let y = blah blah in x + y<br>
<br>
The former will memoize y and share it across all invocations of f1;<br>
whereas f2 will recompute y for each invocation.<br>
<br>
In principle, we could translate between these two forms (the f2 ==> f1<br>
direction requires detecting that y does not depend on x). However, in<br>
practice, the compiler has no way to decide which one is better since it<br>
involves a space/time tradeoff which: (a) requires the language to keep<br>
track of space and time costs, (b) would require whole-program analysis to<br>
determine the total space/time costs, and (c) requires the user's<br>
objective function to know how to weight the tradeoff ratio.<br>
<span class="HOEnZb"><font color="#888888"><br>
--<br>
Live well,<br>
~wren<br>
</font></span><div class="HOEnZb"><div class="h5"><br>
<br>
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</div></div></blockquote></div><br></div>