[Haskell-cafe] Re: Mysterious fact
Andrew Coppin wrote:
> The other day, I accidentally came up with this:
>
> |{-# LANGUAGE RankNTypes #-}
>
> type Either x y= forall r. (x -> r) -> (y -> r) -> r
>
> left :: x -> Either x y
> left x f g= f x
>
> right :: y -> Either x y
> right y f g= g y
>
> This is one example; it seems that just about any algebraic type can
> be encoded this way. I presume that somebody else has thought of this
> before. Does it have a name?
You may want to have a look at my contstuff library, which implements
all the usual monads in CPS:
http://hackage.haskell.org/package/contstuff
This is just the style you implemented Either in, but slightly more
general and with an explicit result type parameter:
newtype EitherT r e m a =
EitherT {
getEitherT :: (a -> m r) -> (e -> m r) -> m r
}
Greets,
Ertugrul
--
nightmare = unsafePerformIO (getWrongWife >>= sex)
http://ertes.de/
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[Haskell-cafe] Re: Mysterious fact
Lennart Augustsson writes: > Jon, you beat me to it. I was going to mention Ponder. Strange chance; yesterday was the first time I read haskell café for something like half a year. > But Ponder did have a builtin type, it had the function type built in. :) Well, to use the nomenclature of Ponder itself, (->) is a type /generator/, not a type. So either it had no built-in types, or it had infinitely many ;-) -- Jón Fairbairn jon.fairba...@cl.cam.ac.uk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Mysterious fact
Jon, you beat me to it. I was going to mention Ponder.
But Ponder did have a builtin type, it had the function type built in. :)
-- Lennart
On Tue, Nov 2, 2010 at 9:47 PM, Jon Fairbairn
wrote:
> Andrew Coppin writes:
>
>> The other day, I accidentally came up with this:
>>
>> |{-# LANGUAGE RankNTypes #-}
>>
>> type Either x y= forall r. (x -> r) -> (y -> r) -> r
>>
>> left :: x -> Either x y
>> left x f g= f x
>>
>> right :: y -> Either x y
>> right y f g= g y
>>
>> |
>>
>> This is one example; it seems that just about any algebraic
>> type can be encoded this way. I presume that somebody else
>> has thought of this before. Does it have a name?
>
> You could try reading my PhD thesis!
>
> contains a link to the full text scanned to a pdf. (That -- 1985
> -- was a long time ago. One thing I really regret about it is
> that there should have been a comma between "simple" and "typed"
> in the title. I suspect people think "simply typed" when they
> see it). It isn't hard to read (one of my examiners said it made
> good bed-time reading).
>
> Anyway, the relevant part is that Ponder was a programming
> language (Stuart Wray even wrote a GUI programme in it) that had
> (in principle) no built-in types, relying on the type system
> being powerful enough to express anything and the optimiser
> being good enough to convert them to something more sensible.
> In practice neither was /quite/ true, but it got quite close.
>
> --
> Jón Fairbairn jon.fairba...@cl.cam.ac.uk
> http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2010-09-14)
>
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[Haskell-cafe] Re: Mysterious fact
Andrew Coppin writes:
> The other day, I accidentally came up with this:
>
> |{-# LANGUAGE RankNTypes #-}
>
> type Either x y= forall r. (x -> r) -> (y -> r) -> r
>
> left :: x -> Either x y
> left x f g= f x
>
> right :: y -> Either x y
> right y f g= g y
>
> |
>
> This is one example; it seems that just about any algebraic
> type can be encoded this way. I presume that somebody else
> has thought of this before. Does it have a name?
You could try reading my PhD thesis!
contains a link to the full text scanned to a pdf. (That -- 1985
-- was a long time ago. One thing I really regret about it is
that there should have been a comma between "simple" and "typed"
in the title. I suspect people think "simply typed" when they
see it). It isn't hard to read (one of my examiners said it made
good bed-time reading).
Anyway, the relevant part is that Ponder was a programming
language (Stuart Wray even wrote a GUI programme in it) that had
(in principle) no built-in types, relying on the type system
being powerful enough to express anything and the optimiser
being good enough to convert them to something more sensible.
In practice neither was /quite/ true, but it got quite close.
--
Jón Fairbairn jon.fairba...@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2010-09-14)
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