|
| | -Original Message-
| | From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
| | Sent: 21 March 2003 04:19
| | To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
| | Subject: Re: simulating dynamic dispatch
| |
| |
| | i'm hoping to be able to simulate a sort of dynamic dispatch
based
| on
| | class
http://research.microsoft.com/~simonpj/papers/hmap/
The technique you describe in that paper is exactly what I was
wanting for many times. I often stopped using algebraic data types
because of the immense amount of boilerplate I had to introduce.
Thanks!
But now I have a question regarding
Interestingly, when I want hugs to show me the type
of
fun::(forall a.[a]-Int)-[b]-[c]-Int
it tells me: ERROR - Use of fun requires at least 1 argument
Why that? At least I have explicitely specified the type.
Hmm, ghci behaves properly.
But using hugs I get the same error :-(.
No idea!
Thanks! These examples and counterexamples help a lot
in understanding.
Markus
The reason is that sum only works on integer lists, whereas the given
type for fun requires that the first argument be a function that works
on lists of any type, such as length.
If sum were allowed as argument
I think you are looking like something done in the
HTML-Combinator-libraries.
I tried something like that some time ago, but didn't finish. But perhaps
you
can get an idea from that. See the files with this mail. (The code is in
unknown condition.)
Markus
ah, yes. i was aware that would work.
://research.microsoft.com/~simonpj/papers/hmap/
I'm not certain, but it has the right smell.
Simon
| -Original Message-
| From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
| Sent: 21 March 2003 04:19
| To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
| Subject: Re: simulating dynamic dispatch
i'm hoping to be able to simulate a sort of dynamic dispatch based on
class instances.
It seems you want to dispatch based not on a type but on the
constraint of a type.
You code almost worked. Here's the a bit updated and working version.
class Foo a where { foo :: a - Bool }
class Bar a
-- *Main test $ MkFoo (0::Int)
-- Just True
-- *Main test $ MkFoo (10::Int)
-- Just False
-- *Main test $ MkBar 'a'
-- Just True
-- *Main test $ MkBar 'b'
-- Just False
ah, yes. i was aware that would work. i forgot to mention the constraint
that i don't want the user to have to
On 20-Mar-2003, Hal Daume III [EMAIL PROTECTED] wrote:
i'm hoping to be able to simulate a sort of dynamic dispatch based on
class instances. basically a function which takes a value and depending
on what classes it is an instance of, does something.
I call this feature dynamic type class
