Look also at safe package http://hackage.haskell.org/package/safe 2012/3/13 Chris Wong

On Tue, Mar 13, 2012 at 12:24 PM, Chris Smith wrote:

...

On Mon, Mar 12, 2012 at 3:14 PM, Kevin Clees wrote:

...

Now my function looks like this:

tmp:: [(Int, Int)] -> Int -> (Int, Int) tmp [] y = (0,0) tmp xs y = xs !! (y-1)

Just a warning that this will still crash if the list is non-empty by the index exceeds the length. That's because your function is no longer recursive, so you only catch the case where the top-level list is empty. The drop function doesn't crash when dropping too many elements though, so you can do this and get a non-recursive function that's still total:

tmp :: [(Int,Int)] -> Int -> (Int, Int) tmp xs y = case drop (y-1) xs of [] -> (0,0) Just (x:_) -> x

That last line should be

(x:_) -> x

without the "Just". Hopefully that'll save a bit of confusion.

Chris

...

-- Chris Smith

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe