On Sat, Feb 20, 2010 at 9:10 PM, Andrew Coppin
wrote:
> PS. Epic, epic comment spam.
Yeah, sorry. Every now and again I decide I should deal with it. Then
I rediscover that it takes about four clicks to delete each comment.
Basically, I leave my blog alone until I have something (hopefully)
inter
Stephen Tetley wrote:
Hi Andrew
"Spot the difference"
data Property x y = forall s. Property s (x -> s -> s) (s -> y)
data Fold b c = forall a. F (a -> b -> a) a (a -> c)
The later is from:
http://squing.blogspot.com/2008/11/beautiful-folding.html
Max Rabkin's is is closer to the original ar
Hi Andrew
"Spot the difference"
data Property x y = forall s. Property s (x -> s -> s) (s -> y)
data Fold b c = forall a. F (a -> b -> a) a (a -> c)
The later is from:
http://squing.blogspot.com/2008/11/beautiful-folding.html
Max Rabkin's is is closer to the original argument ordering of foldl
Anyway, for yours: try to implement (.) :: Property b c -> Property a
b -> Property a c, and first :: Property a b -> Property (a,c) (b,c).
Then you will have an arrow.
(.) = flip (>==>)
first p = p >==< pure id
No, not quite.
\p -> p >==< pure id :: Property a b -> Property a (b, a)
W
Luke Palmer wrote:
On Sat, Feb 20, 2010 at 3:30 AM, Andrew Coppin
wrote:
Have I just invented arrows?
No... you have a data type which is *an* Arrow (probably/almost).
Well, OK, that's kind of what I meant. ;-)
The
pure implementation bugs me because of its use of undefined. Migh
On Sat, Feb 20, 2010 at 3:30 AM, Andrew Coppin
wrote:
> Have I just invented arrows?
No... you have a data type which is *an* Arrow (probably/almost). The
pure implementation bugs me because of its use of undefined. Might
still be okay though. I would be more comfortable if it could not
output
The other day, I found myself writing the following code:
data Property x y = forall s. Property s (x -> s -> s) (s -> y)
step :: x -> Property x y -> Property x y
step x (Property s f g) = Property (f x s) f g
read :: Property x y -> y
read (Property s _ g) = g s
pure :: (x -> y) -> Property
