le to make Foo values where the parameter type isn't
> in Ord, too. I just want unFoo to work on specific Foo values where it is.
>
> -Original Message-
> From: Claus Reinke [mailto:[EMAIL PROTECTED]
> Sent: 27 March 2008 12:25
> To: Sittampalam, Ganesh; Ganes
> > Because I want to be able to make Foo values where the parameter type
> > isn't in Ord, too. I just want unFoo to work on specific Foo values where
> > it is.
> but your recursive function requires a recursive constraint, which your data
> type does not guarantee byconstruction, and which
Because I want to be able to make Foo values where the parameter type isn't in Ord, too. I just
want unFoo to work on specific Foo values where it is.
but your recursive function requires a recursive constraint,
which your data type does not guarantee by construction,
and which the Ord instances
am
Cc: glasgow-haskell-users@haskell.org
Subject: Re: flexible contexts and context reduction
perhaps i'm missing something but, instead of trying to deduce conditions from
conclusions, why can't you just follow ghc's suggestion, and add the
constraints to the constructor?
data
perhaps i'm missing something but, instead of trying to deduce
conditions from conclusions, why can't you just follow ghc's
suggestion, and add the constraints to the constructor?
data Foo a where
Foo1 :: a -> Foo a
Foo2 :: (Ord a,Ord b) => Foo a -> Foo b -> Foo (a, b)
(possibly with another
> If you write the instance
> instance Theta => Foo (T a b) where ...
> where Theta is an arbitrary context, then, given a dictionary for (Foo (T a
> b)), you can get dictionaries for each constraint in Theta. Or in logic
>
>Theta <=> Foo (T a b)
>
> In your example, Theta is em
27;; Ganesh Sittampalam
Cc: glasgow-haskell-users@haskell.org; Martin Sulzmann
Subject: RE: flexible contexts and context reduction
Why "unfortunately"? Looks fine to me.
Simon
|
| Unfortunately, GHC accepts the following:
|
| {-# LANGUAGE FlexibleInstances #-}
| module Foo2 where
|
| data
ttampalam
| Cc: glasgow-haskell-users@haskell.org; Martin Sulzmann
| Subject: RE: flexible contexts and context reduction
|
| Why "unfortunately"? Looks fine to me.
|
| Simon
|
| |
| | Unfortunately, GHC accepts the following:
| |
| | {-# LANGUAGE FlexibleInstances #-}
| | module Foo2
lasgow-haskell-users@haskell.org; Martin Sulzmann
Subject: RE: flexible contexts and context reduction
Why "unfortunately"? Looks fine to me.
Simon
|
| Unfortunately, GHC accepts the following:
|
| {-# LANGUAGE FlexibleInstances #-}
| module Foo2 where
|
| data Foo = Foo
| deriving Eq
|
|
Why "unfortunately"? Looks fine to me.
Simon
|
| Unfortunately, GHC accepts the following:
|
| {-# LANGUAGE FlexibleInstances #-}
| module Foo2 where
|
| data Foo = Foo
| deriving Eq
|
| instance Ord (Foo, Foo) where
| (Foo, Foo) < (Foo, Foo) = False
__
Tom Schrijvers wrote:
> On Wed, 26 Mar 2008, Ganesh Sittampalam wrote:
>> On Wed, 26 Mar 2008, Ross Paterson wrote:
>>
>>> On Wed, Mar 26, 2008 at 08:52:43PM +, Ganesh Sittampalam wrote:
I'm a bit confused about why the following program doesn't compile
(in any of 6.6.1, 6.8.1 and
> So the other question is whether this is useful. How often do people write
> stuff like this?
>f :: Ord [a] => a -> a -> Bool
>f x y = x>y
> Nevertheless, I hadn't realised it was possible before, and now I can see it
> is.
A closer example to what I was actually doing was th
You're talking about something else: the dictionaries (Ord a, Ord b) from which the Ord
(a,b) dictionary were constructed. We don't have a very good name for these guys, but
"superclass" isn't a good one.
Otherwise I agree with all you say. Your idea of using type families is cool.
|
| >> To use bar, you need (Ord a, Ord b). You're assuming that Ord (a, b)
| >> implies that, but it's the other way round.
|
| Logically, the implication holds. There's an equivalence:
|
| Ord a /\ Ord b <=> Ord (a,b)
|
...
| The problem with dictionaries is that you have to store the supe
On Wed, 26 Mar 2008, Ganesh Sittampalam wrote:
On Wed, 26 Mar 2008, Ross Paterson wrote:
On Wed, Mar 26, 2008 at 08:52:43PM +, Ganesh Sittampalam wrote:
I'm a bit confused about why the following program doesn't compile (in
any of 6.6.1, 6.8.1 and 6.9.20080316). Shouldn't the Ord (a, b) c
On Wed, 26 Mar 2008, Ross Paterson wrote:
On Wed, Mar 26, 2008 at 08:52:43PM +, Ganesh Sittampalam wrote:
I'm a bit confused about why the following program doesn't compile (in
any of 6.6.1, 6.8.1 and 6.9.20080316). Shouldn't the Ord (a, b) context
be reduced?
To use bar, you need (Ord a,
On Wed, Mar 26, 2008 at 08:52:43PM +, Ganesh Sittampalam wrote:
> I'm a bit confused about why the following program doesn't compile (in
> any of 6.6.1, 6.8.1 and 6.9.20080316). Shouldn't the Ord (a, b) context
> be reduced?
>
> {-# LANGUAGE FlexibleContexts #-}
>
> module Test2 where
>
> foo
Hi,
I'm a bit confused about why the following program doesn't compile (in any
of 6.6.1, 6.8.1 and 6.9.20080316). Shouldn't the Ord (a, b) context be
reduced?
Cheers,
Ganesh
{-# LANGUAGE FlexibleContexts #-}
module Test2 where
foo :: Ord (a, b) => (a, b) -> (a, b)
foo = bar
bar :: (Ord a
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