[Haskell-beginners] How do I return Nothing from a function?
kc1956 at gmail.com
Mon Apr 21 17:53:31 UTC 2014
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
*Main> :t weight
:: (Ix t1, Ix t2) => t1 -> t2 -> Array (t1, t2) (Maybe t) -> t
weight x y g = w
(Just w) = g!(x,y)
Thank you for your time.
Sent from an expensive device which will be obsolete in a few months! :D
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