[Haskell-cafe] Tutorial: Haskell for the Evil Genius

[Benjamin L. Russell]

> I found some useful reference code on the Haskell Wiki and constructed my own
> memoized Fibonacci function using the MemoTrie library, which, fortunately, is
> builtin with Haskell Platform and therefore does not require the tutorial
> reader to install additional code.
>
> The new version of the tutorial includes an ordinary recursive Fibonacci
> function (fib1.hs), and the same code but renamed to fib', memoized using the
> memo function from the MemoTrie library (fib2.hs), and exposed as fib. Unix
> time information provides real numbers for comparison: The memoized version is
> clearly much faster.
>
> I rewrote the section, deleting the part that stated memoization was automatic,
> and added text describing how Haskell makes memoization easy.

Which version of the Haskell Platform are you using?  I tried running
your memoized Fibonacci function that uses the MemoTrie library on
Windows XP with Service Pack 3, and received the following error
message:

> $>./runhaskell fib2

> fib2.hs:3:7:
>     Could not find module `Data.Memotrie':
>       Use -v to see a list of the files searched for.

My version is as follows:

> $>./ghci -v
> GHCi, version 6.12.3: http://www.haskell.org/ghc/  :? for help
> Glasgow Haskell Compiler, Version 6.12.3, for Haskell 98, stage 2 booted by GHC
> version 6.10.4
> Using binary package database: C:\PROGRA~1\HASKEL~1\201020~1.0\lib\package.conf.
> d\package.cache
> hiding package base-3.0.3.2 to avoid conflict with later version base-4.2.0.2
> wired-in package ghc-prim mapped to ghc-prim-0.2.0.0-2feb0cb38f65a4827135ada88c3
> 4f3ef
> wired-in package integer-gmp mapped to integer-gmp-0.2.0.1-72436e28c79d056c87cc0
> d2d2f9f3773
> wired-in package base mapped to base-4.2.0.2-0d1804f62045e52b2e806996d84f5318
> wired-in package rts mapped to builtin_rts
> wired-in package haskell98 mapped to haskell98-1.0.1.1-b5196101fd7a8c42a8d53bd80
> 33d6765
> wired-in package template-haskell mapped to template-haskell-2.4.0.1-401621dedd4
> a5f07bfd8630247358bf5
> wired-in package dph-seq mapped to dph-seq-0.4.0-be069f0bb710922a6ddd4ed2b91e3a6
> c
> wired-in package dph-par mapped to dph-par-0.4.0-b31a0ce10b7c92126978fcc929077ad
> 6
> Hsc static flags: -static
> Loading package ghc-prim ... linking ... done.
> Loading package integer-gmp ... linking ... done.
> Loading package base ... linking ... done.
> Loading package ffi-1.0 ... linking ... done.

For reference, my code is as follows:

> #!"c:/Program Files/Haskell Platform/2010.2.0.0/bin/" runhaskell

> import Data.Memotrie (memo)

> fib :: Int -> Int
> fib = memo fib'
>     where
>         fib' :: Int -> Int
>         fib' 0 = 0
>         fib' 1 = 1
>         fib' n = fib' (n - 1) + fib' (n - 2)

> main :: IO ()
> main = do
>   putStrLn (show (fib 30))

Thank you.

-- Benjamin L. Russell
-- 
Benjamin L. Russell  /   DekuDekuplex at Yahoo dot com
http://dekudekuplex.wordpress.com/
Translator/Interpreter / Mobile:  +011 81 90-6526-1406
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