Keith Wansbrough [EMAIL PROTECTED] wrote in article [EMAIL PROTECTED] in
gmane.comp.lang.haskell.general:
module TypedFM where
data FM k -- Abstract; finite map indexed bykeys of type k
data Key k a -- Abstract; a key of type k, indexing a value of type a
empty
| If you use Simon PJ's type signatures, you can't really disallow using
| a key from one map with another map.
Yes, that's a good point. So there are really three issues:
a) single-threaded-ness
b) making sure you look up in the right map
c) making sure the thing you
Yes, that's a good point. So there are really three issues:
a) single-threaded-ness
b) making sure you look up in the right map
c) making sure the thing you find has the right type
Even if you have typed keys, (Key a), then if you look them up in the
wrong map, any
In article [EMAIL PROTECTED],
[EMAIL PROTECTED] (Carl R. Witty) wrote:
Here's a hand-waving argument that you need either Typeable (or
something else that has a run-time concrete representation of types)
or ST/STRef (or something else, probably monadic, that can track
unique objects) to do
In article [EMAIL PROTECTED],
[EMAIL PROTECTED] (Carl R. Witty) wrote:
Here's a hand-waving argument that you need either Typeable (or
something else that has a run-time concrete representation of types)
or ST/STRef (or something else, probably monadic, that can track
unique objects)
Keith Wansbrough [EMAIL PROTECTED] writes:
In article [EMAIL PROTECTED],
[EMAIL PROTECTED] (Carl R. Witty) wrote:
Here's a hand-waving argument that you need either Typeable (or
something else that has a run-time concrete representation of types)
or ST/STRef (or something else,
Simon Peyton-Jones [EMAIL PROTECTED] writes:
| Conjecture: It's impossible to implement RefMonad directly in Haskell
| without making use of built-in ST or IO functionality and without
unsafe or
| potentially diverging code (such as unsafeCoerce).
A more concrete way to formulate a problem
Derek Elkins wrote:
| The question (at least to me) is more, 'you can
| satisfy the RefMonad interface with STRefs or IORefs,
| but those use imperative features under the hood;
| can it be satisfied without them?'
As I showed in the message that spawned off this discussion,
this is indeed
Someone asked me:
| I don't recall the message you are referring to, and I
| can't find it in the archive. Can you point me at it?
Sorry, I meant:
http://www.haskell.org/pipermail/haskell/2001-September/007922.html
/K :-)
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On Wed, 11 Jun 2003 09:19:46 +0200 (MET DST)
Koen Claessen [EMAIL PROTECTED] wrote:
Derek Elkins wrote:
| The question (at least to me) is more, 'you can
| satisfy the RefMonad interface with STRefs or IORefs,
| but those use imperative features under the hood;
| can it be satisfied
update :: (Typable b) = FM k - Key k a - b - (FM ...)
I didn't know constraints on values are allowed... Given below is the
implementation of the required interface, in Haskell98
module TypedFM where
data FM k -- Abstract; finite map indexed bykeys of type k
data Key k
On Tue, 10 Jun 2003 11:44:45 -0700 (PDT)
[EMAIL PROTECTED] wrote:
update :: (Typable b) = FM k - Key k a - b - (FM ...)
I didn't know constraints on values are allowed... Given below is the
implementation of the required interface, in Haskell98
They aren't presumably as that would (as
Ralf Hinze writes:
Why is that? Ok, here is my second implementation. It uses the
Dynamic module from our HW2002 paper. A key is a pair consisting
of the actual key and a type representation.
[..]
update:: (Typable b) = FM k - Key k a - b - (FM k, Key
k b)
Simon P.J. writes:
... So it's reasonable that there should be some language extension.
I'm just looking for the minimal such extension.
unsafeCoerce# is quite a minimal extension :-)
Cheers,
Simon
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[EMAIL
A more concrete way to formulate a problem that I believe to be
equivalent is this. Implement the following interface
module TypedFM where
data FM k -- Abstract; finite map indexed by keys
of type k
data Key k a-- Abstract; a key of type k, indexing
insert return a key.
S
| -Original Message-
| From: Ralf Hinze [mailto:[EMAIL PROTECTED]
| Sent: 06 June 2003 14:12
| To: Simon Peyton-Jones; Tim Sweeney; [EMAIL PROTECTED]; Ashley
Yakeley
| Subject: Re: Typesafe MRef with a regular monad
|
| A more concrete way to formulate a problem
Am Freitag, 6. Juni 2003 15:23 schrieb Simon Peyton-Jones:
Oh bother, I forgot to add that you can of course insert a new value
with an old key (suitably typed) and have it overwrite. Else, as you
say, there would not be much point.
Maybe it'd be better to have a separate key-construction
such extension. Finite maps see a bit of a big
hammer.
Simon
| -Original Message-
| From: Ralf Hinze [mailto:[EMAIL PROTECTED]
| Sent: 06 June 2003 14:29
| To: Simon Peyton-Jones; Tim Sweeney; [EMAIL PROTECTED]; Ashley
Yakeley
| Subject: Re: Typesafe MRef with a regular monad
|
| Am
Am Freitag, 6. Juni 2003 15:47 schrieb Simon Peyton-Jones:
Yes, one *could* use dynamic types. But the check would always succeed!
Why is that? If I overwrite an entry with a value of a different type,
then the check fails. I am certainly missing something ...
Cheers, Ralf
; Tim Sweeney; [EMAIL PROTECTED]; Ashley
Yakeley
| Subject: Re: Typesafe MRef with a regular monad
|
| Am Freitag, 6. Juni 2003 15:47 schrieb Simon Peyton-Jones:
| Yes, one *could* use dynamic types. But the check would always
succeed!
|
| Why is that? If I overwrite an entry with a value
Am Freitag, 6. Juni 2003 16:09 schrieb Simon Peyton-Jones:
You can't overwrite an entry with a value of a different type, because
the keys are typed! Any more than you can overwrite an IORef with a
value of a different type.
S
Why is that? Ok, here is my second implementation. It uses the
In fact I think these Typesafe MRef's are exactly equivalent
to dynamic types. In other words, if you've got one,
you've got the other. Ralf Hinze has just shown that
if you have dynamic types you can implement Typesafe MRef.
The reverse implementation would be something like
data Dynamic = FM
-
From: Ashley Yakeley [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Wednesday, June 04, 2003 5:19 PM
Subject: Re: Typesafe MRef with a regular monad
In article [EMAIL PROTECTED],
[EMAIL PROTECTED] wrote:
Ashley Yakeley wrote:
] ] Is it possible to actually implement a working instance
On Wed, 04 Jun 2003 15:19:53 -0700
Ashley Yakeley [EMAIL PROTECTED] wrote:
In article [EMAIL PROTECTED],
[EMAIL PROTECTED] wrote:
Ashley Yakeley wrote:
] ] Is it possible to actually implement a working instance of
RefMonad in ] ] Haskell, without making use of a built-in monad like
In article [EMAIL PROTECTED],
Derek Elkins [EMAIL PROTECTED] wrote:
M = (forall s.ST s)
R = STRef s
e.g. runST :: (forall s.ST s a) - a
you can use the same trick for your own RefMonad. I'm not sure if this
will work with RefMonad exactly. If ST/STRef can be made an instance of
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