[Haskell-cafe] memoization

[KC]

Have you tried the compiler?


On Sun, Jul 21, 2013 at 11:59 PM, Christopher Howard <
christopher.howard at frigidcode.com> wrote:

>  When I previously asked about memoization, I got the impression that
> memoization is not something that just happens magically in Haskell. Yet,
> on a Haskell wiki page about Memoization<http://www.haskell.org/haskellwiki/Memoization#Memoization_with_recursion>,
> an example given is
>
>  memoized_fib :: Int -> Integer
> memoized_fib = (map fib [0 ..] !!)
>    where fib 0 = 0
>          fib 1 = 1
>          fib n = memoized_fib (n-2) + memoized_fib (n-1)
>
>
> I guess this works because, for example, I tried "memoized_fib 10000" and
> the interpreter took three or four seconds to calculate. But every
> subsequent call to "memoized_fib 10000" returns instantaneously (as does
> "memoized_fib 10001").
>
> Could someone explain the technical details of why this works? Why is "map
> fib [0 ..]" not recalculated every time I call memoized_fib?
>
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>


-- 
--
Regards,
KC
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