[Haskell-beginners] Re: Code help requested

[Brandon S. Allbery KF8NH]

On Jan 15, 2010, at 20:17 , Tim Perry wrote:
> binary_find list elem =
>  do_search list elem 0 (length list -1)
>  where
>    do_search list elem low high
>      | high < low = Nothing
>      | midVal > elem = do_search list elem low (mid - 1)
>      | midVal < elem = do_search list elem (mid + 1) high
>      | otherwise = Just mid
>      where
>        midVal = list !! mid
>        mid = low + (high - low) `div` 2


Observation:  the first two parameters to do_search never change  
within an invocation of binary_find, and the corresponding arguments  
to binary_find are in scope; depending on the (lack of) cleverness of  
the compiler, you could see a speedup by not passing them around  
unnecessarily.  In addition, it's *conceptually* cleaner because  
passing them around explicitly suggests to someone reading the source  
that they *do* change when that isn't actually the case.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


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