On 2 Nov 2009, at 00:11, Ross Paterson wrote:
On Sun, Nov 01, 2009 at 04:20:18PM +0000, Conor McBride wrote:
On 31 Oct 2009, at 10:39, Conor McBride wrote:
I have an example, perhaps not a datatype:
tomorrow-you-will-know
Elaborating, one day later,
if you know something today, you can arrange to know it tomorrow
if will know a function tomorrow and its argument tomorrow, you
can apply them tomorrow
but if you will know tomorrow that you will know something the
day after, that does not tell you how to know the thing tomorrow
Yes, but if you will know tomorrow that you will know something
tomorrow, then you will know that thing tomorrow.
That depends on what "tomorrow" means tomorrow.
The applicative does coincide with a monad, just not the one you first
thought of (or/max rather than plus).
True, but it's not the notion I need to analyse circular programs.
I'm looking for something with a fixpoint operator
fix :: (Tomorrow x -> x) -> x
which I can hopefully use to define things like
repmin :: Tree Int -> (Int, Tomorrow (Tree Int))
so that the fixpoint operator gives me a Tomorrow Int which I
can use to build the second component, but ensures that the
black-hole-tastic Tomorrow (Tomorrow (Tree Int)) I also receive
is too late to be a serious temptation.
All the best
Conor
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