On 8 Jan 2011, at 15:27, Henning Thielemann wrote:
On Sat, 8 Jan 2011, Conor McBride wrote:
On 8 Jan 2011, at 11:14, Henning Thielemann wrote:
For me, the solutions of Dave Menendez make most sense: Generalize
Maybe to Foldable and List to MonadPlus.
What has it to do with monads? There's no bind in sight.
I see a '>>=' in front of each of his expressions.
That'll teach me to wake up first. Sorry.
If you have some m (f x), and you make an (m x) from each
inner x, then you do need something joiny.
Of course, there is an alternative generalisation.
[] and Maybe are both Foldable, hence so is their composition.
There's got to be a thing of type
collapse :: (Foldable f, Alternative a) => f x -> a x
which would do the job.
Of course, anything which is both foldable and alternative
certainly has a function with the type of join.
Cheers
Conor
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