[Haskell-cafe] efficient chop

[Thomas DuBuisson]

This was a recent question on StackOverflow:

http://stackoverflow.com/questions/6270324/in-haskell-how-do-you-trim-whitespace-from-the-beginning-and-end-of-a-string/6270382#6270382

Where I started:

If you have serious text processing needs then use the text package
from hackage.

And concluded:

A quick Criterion benchmark tells me that (for a particularly long
string of words with spaces and ~200 pre and post spaces) my trim
takes 1.6 ms, the trim using reverse takes 3.5ms, and Data.Text.strip
takes 0.0016 ms.

Cheers,
Thomas

On Tue, Sep 13, 2011 at 8:03 PM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:
> Hello Cafe,
>
> I would like to have an efficient implementation of the chop function.
> As you guess, the chop function drops spaces in the tail of a list.
>
>   chop " foo  bar baz   "
>   ->   " foo  bar baz"
>
> A naive implementation is as follows:
>
>    chopReverse :: String -> String
>    chopReverse = reverse . dropWhile isSpace . reverse
>
> But this is not elegant. foldr version is as follows:
>
>    chopFoldr :: String -> String
>    chopFoldr = foldr f []
>      where
>        f c []
>          | isSpace c = []
>          | otherwise = c:[]
>        f c cs = c:cs
>
> But this code is slower than chopReverse in some cases.
>
> Are there any more efficient implementations of chop? Any suggestions?
>
> --Kazu
>
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