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