[Haskell-cafe] "computational time" always 0.0 in this example...

[Lemmih]

On 12/7/06, Lennart <lray at l-ray.de> wrote:
> Hi,
>
> with the following code, I want to measure the time being needed to
> execute the algorithm. But the result is always 0.0.
>
> import Char (toLower)
> import Maybe
> import List ( delete, sort, intersect )
> import System.CPUTime
> import Control.Exception
>
> import Debug.Trace
>
> fromInt = fromIntegral
>
> wordList2 :: [String]
> wordList2 = ["Sam J Chapman",
>        "Samuel Chapman",
>        "S Chapman",
>        "Samuel John Chapman",
>            "John Smith",
>        "Richard Smith",
>        "aaaa mnop zzzz",
>        "bbbb mnop yyyy",
>        "aa mnop zzzzzz",
>        "a ",
>        "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
>        "aaaa bcdefgh mmmmmmmm stuvwx zzzzzz",
>        "jjjj bcdefgh qqqqqqqq stuvx yyyyyy",
>        "aaaaa bcdefgh stuvwx zzzzzz",
>        "aaaaa aaaaa aaaaa zzzzzz",
>        "aaaaa aaaaa"]
>
> time :: IO t -> IO t
> time a = do
>    start <- getCPUTime
>    v <- a
>    end   <- getCPUTime
>    let diff = (fromIntegral (end - start)) / (10^12)
> --    let diff = (fromIntegral (end - start))
>    putStrLn "Computation time:"
>    print (diff :: Double)
>    return v
>
> main = do
>         putStrLn "Starting..."
>         time $ doTest wordList2 wordList2 `seq` return ()
>         putStrLn "Done."
>
> test3 = let loop = getCPUTime >>= print >> loop in loop
>
> doTest :: [String] -> [String] -> [ Double ]
> doTest [] _ = []
> doTest (x:xs) [] = doTest xs xs
> doTest (x:xs) (y:ys) = result : (doTest (x:xs) (ys))
>                         where result =  qGramMetrics2 x y
>
> qGramMetrics2:: String -> String -> Double
> qGramMetrics2 t1 t2 = let i = intersect (qGramList (map toLower t1) 3)
> (qGramList (map toLower t2) 3)
>                  il = fromInt (length i)
>              ml = fromInt ((max (length t1) (length t2)) - 1 )
>              in (il / ml )
>
> -- list of chars within list of qgrams
> qGramList :: String -> Int -> [[Char]]
> qGramList [] _        = []
> qGramList (x:[]) _     = []
> qGramList (x:xs) i1    = (x: take (i1 - 1) xs):(qGramList xs i1)
>
> -- list of chars within list of qgrams
> numberedQgramListWithStart :: String -> Int -> [(Int, [Char])]
> numberedQgramListWithStart x i1 = let prefix = replicate (i1-1) '#'
>                      suffix = replicate (i1-1) '$'
>                        in numberedQgramList (prefix++(x++suffix)) i1 0
>
> numberedQgramList :: String -> Int -> Int -> [(Int, [Char])]
> numberedQgramList [] _ _    = []
> numberedQgramList (x:xs) i1 i2
>            -- add the dollar-sign
>            | (length xs) < i1 && x=='$'= []
>            | otherwise = (i2,(x: take (i1 - 1) xs)):(numberedQgramList
> xs i1 (i2+1))
>
> Am using ghci 6.6 under a Kubuntu 6.10 Linux.
>
> time $ product [1..1000] `seq` return ()
> instead of
> time $ doTest wordList2 wordList2 `seq` return ()
> works fine.
>
> things like
> time $ print (doTest wordList2 wordList2) `seq` return () or
> time $ length (doTest wordList2 wordList2) `seq` return () or
> time $ trace (doTest wordList2 wordList2) `seq` return ()
> didn't work.
>
> Am desperated...

Running 'doTest wordList2 wordList2' takes less than 0.00s. Find a
more time consuming function and you will be fine.
Also, have a look at ':set +s' in ghci
(http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-set.html).

-- 
Cheers,
  Lemmih