[Haskell-cafe] Re: Mysterious fact
Andrew Coppin andrewcop...@btinternet.com 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 lenn...@augustsson.net 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
[Haskell-cafe] Re: Mysterious fact
Andrew Coppin andrewcop...@btinternet.com 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!
http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-75.html
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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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
jon.fairba...@cl.cam.ac.uk wrote:
Andrew Coppin andrewcop...@btinternet.com 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!
http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-75.html
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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