Have you tried the compiler? On Sun, Jul 21, 2013 at 11:59 PM, Christopher Howard < christopher.howard@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 Memoizationhttp://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