Thanks, it make sense here. However, like I want to choose s[1,3,6,10] or something like this. Are there some straightforward function or operator for doing this job? The !! operator in haskell seems does not support multiple indecies. Hank Stefan O wrote:

On Thu, Nov 30, 2006 at 05:47:43PM -0800, Huazhi (Hank) Gong wrote:

...

Like given a string list s="This is the string I want to test", I want to get the substring. In ruby or other language, it's simple like s[2..10], but how to do it in Haskell?

Use take and drop, from the Prelude:

(ghci session) Prelude> "Hello world" "Hello world" Prelude> drop 3 "Hello world" "lo world" Prelude> take 7 (drop 3 "Hello world") "lo worl" Prelude> _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Your curious example suggests you might be solving a more specialized problem, like selecting the diagonal of a flattened matrix. In this case, there are much better (and more efficient) data structures that enforce invariants (like squareness of a matrix), if that is what you in fact are doing. Taral wrote:

On 11/30/06, Huazhi (Hank) Gong wrote:

...

Thanks, it make sense here. However, like I want to choose s[1,3,6,10] or something like this. Are there some straightforward function or operator for doing this job? The !! operator in haskell seems does not support multiple indecies.

If you're trying to do random access on a list, you should rethink why you're using a list.

Good. I personally perfer this solution... Bulat Ziganshin-2 wrote:

Hello Huazhi,

Friday, December 1, 2006, 5:04:10 AM, you wrote:

...

However, like I want to choose s[1,3,6,10] or something like this. Are there some straightforward function or operator for doing this job? The !! operator in haskell seems does not support multiple indecies.

just change your mind, Neo ;)

Hugs> map ("abcdefg" !!) [1,3,6] "bdg" :: [Char]

-- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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