Re: [Haskell-cafe] Empty Input list

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

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