[Haskell-cafe] Function hanging in infinite input

martin martin.drautzburg at web.de
Sun Apr 26 19:23:56 UTC 2015

Am 04/26/2015 um 08:38 PM schrieb Matthew Korson:
> The problem is that tAppend is too strict; it evaluates both its arguments before producing anything. This is because
> you are pattern matching on those arguments. You could use lazy patterns or make Temporal a newtype to avoid that. Or
> you could rewrite to something like
>     tAppend as bs = Temporal $ toList as ++ toList bs

Mathew, you made my day!

At least things work now as expected. But could you please elaborate on the difference between

tAppend (Temporal as) (Temporal bs) = Temporal (as ++ bs)


tAppend as bs = Temporal $ (toList as) ++ (toList bs)
toList (Temporal xs) = xs

Why is the first one more strict  than the second?

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