If the result of weight is (Maybe t) instead of the then the result of the
array lookup can be passed out directly for the caller to check:
weight x y g = g!(x, y)
Is this what you mean?
Cheers,
Darren
On Apr 21, 2014 10:53 AM, "KC"
How do I return Nothing from a function?
When there is no edge in the graph this code fails. *** Exception: Graph.hs:65:9-26: Irrefutable pattern failed for pattern (Data.Maybe.Just w)
*Main> :t weight weight :: (Ix t1, Ix t2) => t1 -> t2 -> Array (t1, t2) (Maybe t) -> t
weight x y g = w where (Just w) = g!(x,y)
Thank you for your time.
--
--
Sent from an expensive device which will be obsolete in a few months! :D Casey
_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners