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...
On Mon, Jul 22, 2013 at 4:04 PM, wren ng thornton <w...@freegeek.org> wrote: > On 7/22/13 9:06 AM, Tom Ellis wrote: > > On Mon, Jul 22, 2013 at 07:52:06PM +1200, Chris Wong wrote: > >> A binding is memoized if, ignoring everything after the equals sign, > >> it looks like a constant. > >> > >> In other words, these are memoized: > > [...] > >> f = \x -> x + 1 > > [...] > >> and these are not: > >> > >> f x = x + 1 > > > > In what sense is the former memoised? I'm not aware of any difference > > between these two definitions. > > Consider rather, > > f1 = let y = blah blah in \x -> x + y > > f2 x = let y = blah blah in x + y > > The former will memoize y and share it across all invocations of f1; > whereas f2 will recompute y for each invocation. > > In principle, we could translate between these two forms (the f2 ==> f1 > direction requires detecting that y does not depend on x). However, in > practice, the compiler has no way to decide which one is better since it > involves a space/time tradeoff which: (a) requires the language to keep > track of space and time costs, (b) would require whole-program analysis to > determine the total space/time costs, and (c) requires the user's > objective function to know how to weight the tradeoff ratio. > > -- > Live well, > ~wren > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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