You can't return Nothing, because your function doesn't return a maybe. If you make it a maybe, you just need to return the value of g without further processing.
How do I return Nothing from a function?Thank you for your time.
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)
----
Sent from an expensive device which will be obsolete in a few months! :D
Casey
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