On Thu, Nov 11, 2010 at 06:59:01PM +0200, Markus Läll wrote:
Hi Anonymous W!
As list is a recursive datastructure, you need a recursive (or folding) function to check for duplicates. Right now your function really does accept only two-element lists.
The function would look something like this:
maybeA list@ ((a1,b1) : (a2,b2) : rest) = if hasUniqueKeys list then Just (a1, b1, b2) else Nothing where hasUniqueKeys xs = ... check the list ...
You also need to decide what to do, if the list is empty or contains only one pair.
This is good advice. I would add, however, that I don't think hasUniqueKeys ought to be (directly) recursive. Instead, use functions from the standard libraries to manipulate the list and decide whether it has unique keys. Functions which may be helpful in this task include map, fst, sort, group, length, any. -Brent