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<p class=MsoNormal>I'm new to Haskell and trying to get a better understanding
of sharing (and ultimately memoization). I've read SOE and various of the
tutorials, as well as browsing around the wiki and old mailing lists. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Most of the examples of memoization seem to revolve around
Fibonacci, and are based either on the fact that a list defined within the
function will get shared between calls, or on doing some 'unsafeIO' (which I
haven't dug too deeply into.) <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I've read various discussions that explain why function
calls are generally not automatically memoized (e.g. f x gets
recalculated rather than looked up based on the prior result). The
rationale for that (big space leak and no guarantee of improved performance)
makes sense. (Though I did like one poster's suggestion of a compiler
pragma that hints that a particular function should be memoized.)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I've seen other discussions that suggest that lists are
always shared while in scope (so the fibs trick works). But is that just
a feature of the standard compilers, or is it somewhere mandated in the Hakell
spec (I don't see anything obvious in the Haskell Report tho haven't read it
cover to cover)? <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The wiki page <a
href="http://www.haskell.org/haskellwiki/Performance/Strictness">http://www.haskell.org/haskellwiki/Performance/Strictness</a>
says laziness == non-strictness + sharing but again nowhere gives a set
of rules that guarantees what will be shared and what won't. I was hoping
I might find it here: <a href="http://www.haskell.org/haskellwiki/Sharing">http://www.haskell.org/haskellwiki/Sharing</a>
but no such luck. Or are there no guarantees and you just have to know
how your particular compiler works??<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Cheers,<o:p></o:p></p>
<p class=MsoNormal>Patrick<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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