Thank you oleg.
Sulzmann et al use guards in CHR to turn overlapping heads (instances) into
non-overlapping. Their coherence theorem still assumes non-overlapping.
I agree that what you described is the desirable behaviour when overlapping,
that is to defer the decision when multiple
Coherence (roughly) means that the program's semantics is independent
of the program's typing.
In case of your example below, I could type the program
either use the first or the second instance (assuming
g has type Int-Int). That's clearly bound.
Guard constraints enforce that instances are
I believe that GHC's overlapping instance extensions
effectively uses inequalities.
Why do you think that 'inequalities' model 'best-fit'?
instance C Int -- (1)
instance C a-- (2)
under a 'best-fit' instance reduction strategy
we would resolve C a by using (2).
'best-fit' should
| I believe that GHC's overlapping instance extensions
| effectively uses inequalities.
I tried to write down GHC's rules in the manual:
http://haskell.org/ghc/dist/current/docs/users_guide/type-extensions.htm
l#instance-decls
The short summary is:
- find candidate instances that match
- if
Thank you Martin.
Coherence (roughly) means that the program's semantics is independent
of the program's typing.
In case of your example below, I could type the program
either use the first or the second instance (assuming
g has type Int-Int). That's clearly bound.
If g has type Int-Int, it
It seems that the subject is a bit more complex, and one can force GHC
to choose the less specific instance (if one confuses GHC well
enough): see the example below.
First of all, the inequality constraint is already achievable in
Haskell now: TypeEq t1 t2 False is such a constraint. One can
one can force GHC to choose the less specific instance (if one
confuses GHC well enough): see the example below.
your second example doesn't really do that, though it may look that way.
class D a b | a - b where g :: a - b
instance D Int Bool where g x = True
instance TypeCast Int b = D a b
Sorry to respond to my own message, but I found a much more
satisfactory way to solve this problem. ghc is able to specialize it
so that
data Test1 = Foo | Bar | Baaz | Quux deriving (Enum, Bounded)
sizeTest1 :: (Set Test1) - Int
sizeTest1 = sizeB
compiles into a call directly to
Hello David,
Thursday, April 13, 2006, 12:55:05 AM, you wrote:
Yes, especially curious since the algorithm is taken from AMD's
optimization guide for the Athlon and Opteron series. I'm not good
enough at reading core syntax to be able to see what GHC is doing
with it.
optimization for
On 13 Apr 2006 03:27:03 -, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote:
Creighton Hogg wrote:
No instance for (MatrixProduct a (Vec b) c)
arising from use of `*' at interactive:1:3-5
Probable fix: add an instance declaration for (MatrixProduct a
(Vec b) c)
In
On 2006-04-13, Martin Sulzmann [EMAIL PROTECTED] wrote:
I believe that GHC's overlapping instance extensions
effectively uses inequalities.
Why do you think that 'inequalities' model 'best-fit'?
instance C Int -- (1)
instance C a-- (2)
under a 'best-fit' instance reduction
I grabbed the source code to Haddock, but GHC doesn't like the #if's
and the #endif's. What can I do with these?
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On 4/13/06, Jason Dagit [EMAIL PROTECTED] wrote:
Try using passing -cpp to ghc when you compile.
Jason
Thanks. Will do.
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Creighton Hogg posed the following problem. Given a rather
straightforward matrix multiplication code
-- The elements and the size
data Vec a = Vec (Array Int a) Int deriving (Show,Eq)
type Matrix a = (Vec (Vec a))
class MatrixProduct a b c | a b - c where
(*) :: a - b - c
instance
Hi,
I'm about to start playing with HWS-WP (web server + plugins). It
relies on RuntimeLoader:
http://www.algorithm.com.au/wiki/hacking/haskell.ghc_runtime_loading
I grabbed the example and built it (only one minor tweak to imports
to get it to build) but it doesnt quite work:
$
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