Sorry for the last mail, I now tried it and it returns the next value every
time I call it.
I was using an unsafeperformIO trick somewhere, and that fas the one
resulting in the previously described behaviour.
You can just ignore the previous mail.
2009/12/17 Ozgur Akgun
Maybe not related, but does the following prove next is called once and only once.
import qualified Data.ByteString as BS import qualified Data.ByteString.Char8 as BSC
next = do nextcache <- BS.readFile "next.cache" let nextint = readInt (BSC.unpack nextcache) BS.writeFile "next.cache" (BSC.pack (show (nextint+1))) return nextint
readInt :: String -> Int readInt = read
I put a single character, 1 in the file "next.cache" when I run this through ghci, and call next several times, I always get a 1. Whereas in the file there is a 2. I see that next is a trial of creating a function which returns different things everytime its called, but it's in the IO monad, so that should be doable.
When I re-run ghci, now it starts to give 2 everytime I call it. Does that mean, it doesn't bother to re-read the file while we are in the same process.
Hope it relates to the OP's question in some way :)
Best,
2009/12/16 Daniel Fischer
Am Mittwoch 16 Dezember 2009 15:49:54 schrieb michael rice:
Thanks all,
OK, so this definition of fib
fib 0 = 1 fib 1 = 1 fib n = fib (n-1) + fib (n-2)
would involve a lot of recomputation for some large n,
Where "large" can start as low as 20; 60 would be out of reach.
which memoization would eliminate?
Right.
Michael
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-- Ozgur Akgun
-- Ozgur Akgun