Hi
On Mon, 9 Aug 2004, Simon Peyton-Jones wrote:
Closed classes are certainly interesting, but a better way to go in this
case is to allow the programmer to declear new kinds, as well as new
types. This is what Tim Sheard's language Omega lets you do, and I'm
considering adding it to GHC.
Hi all
With overlapping instances, I'm allowed
class OK x y
instance Functor f = OK (f x) (f y)
instance Functor f = OK x (f y)
but I'm not allowed
class Bad x y z | x y - z
instance Functor f = Bad (f x) (f y) Bool
instance Functor f = Bad x (f y) Int
I don't quite see why.
Hi
Or, more generally,
infixl 9 $
($) :: Monad m = m (s - t) - m s - m t
mf $ ms =
do f - mf
s - ms
return (f s)
or just liftM2 ($)
or just ap
OK, I'm a bad citizen and I never look things up in the library. If it
isn't in the Gentle Introduction
Hi
There's nothing wrong with this in principle; the difficulty is that
when you say
mantissa + 4
you aren't saying which float type to get the mantissa of. Earlier
messages have outlined workarounds, but in some ways the real solution
is to provide a syntax for type application.
Hi
Why is this a duplicate instance declaration:
class C a
class D b
data T a b
instance (C (T a b), C a) = D b
instance (C (T a b), C b) = D a
These are symmetric, but not duplicate, as I see it.
Suppose we add
instance C ()
instance C (T () ())
Now there are two ways to
Hi
Lennart wrote:
I was referring to the expression language.
So this is already allowed:
f :: (forall a . a - a) - (b, c) - (c ,b )
f i (x,y) = (i y, i x)
I'd like to be able to have explicit type applications.
If we denote type application with infix # I'd like to write
f i (x, y)
Hi
On Fri, 5 Apr 2002, Ashley Yakeley wrote:
At 2002-04-04 05:57, C T McBride wrote:
...which would be very useful, but would probably have unpleasant
consequences for type inference...
To my mind, this is not a credible objection. The horse has already
bolted; there's no point
Hi all,
At 2002-04-03 15:14, Hal Daume III wrote:
type FM = FiniteMap
type FM a b = FiniteMap a b
I wasn't aware there was (supposed to be) a difference
between these two declarations? Is there?
On Wed, 3 Apr 2002, Ashley Yakeley wrote:
type FM a b = FiniteMap a b
...This
Hi
On Thu, 28 Feb 2002, Tom Pledger wrote:
C T McBride writes:
| data Fix f = Fix (f (Fix f))
|
| There's no equivalent first-order definition. This is where
| higher-kind parameters actually buy us extra stuff, and it's also the
| point at which the first-order constraint for show
Hi
I'm rather fond of fixpoint constructions like this one:
newtype Copy a = Copy a deriving Show
data Wonky f
= Wonky
| Manky (f (Wonky f))
deriving Show
(Clearly this is an ill-motivated example, but the real example which
caused this problem is available on request...)
The
Hi Simon
On Tue, 5 Feb 2002, Simon Peyton-Jones wrote:
2. I'd be interested to know of any other examples you have of
*bi-directional* functional depenencies. The above simplification
nukes my only convincing example. (Usually one set of
type variables determines another, but
On Wed, 16 May 2001, Stefan Karrmann wrote:
On Tue, May 15, 2001 at 09:14:02PM +0300, Dylan Thurston wrote:
On Tue, May 15, 2001 at 06:33:41PM +0200, Jerzy Karczmarczuk wrote:
Serge Mechveliani :
...
The matter was always in parametric domains ...
Whoever tried to program real
C T McBride wrote:
Hi
This is a long message, containing a program which makes heavy use of
type classes with functional dependencies, and a query about how the
typechecker treats them. It might be a bit of an effort, but I'd be
grateful for any comment and advice more experienced
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