[Haskell-beginners] How do I return Nothing from a function?
timmelzer at gmail.com
Mon Apr 21 18:23:44 UTC 2014
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
Am 21.04.2014 19:53 schrieb "KC" <kc1956 at gmail.com>:
> 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
> :: (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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> Beginners at haskell.org
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