On Wed, Apr 14, 2004 at 06:29:38PM +0200, Tomasz Zielonka wrote:
> >
> > Is it possible to unwrap an existential type in ghci?
>
> For me this seems to be a bug in GHCi.
> I wonder if there a type in Haskell-with-extensions that could be
> assigned to x?
Probably GHCi could do the same as in thi
> > anyway (thus providing the dictionary) there is no point in storing it.
>
> Aren't you talking about a different declaration?
>
> data Show a => Show' a = Show' a
Yes, I am. Oops, sorry.
--KW 8-)
--
Keith Wansbrough <[EMAIL PROTECTED]>
http://www.cl.cam.ac.uk/users/kw217/
University of
On Wed, Apr 14, 2004 at 10:13:51AM -0400, John D. Barnett wrote:
>
> *DepTest> :t Show' True
> Show' True :: Show'
> *DepTest> Show' x <- return $ Show' True
> *DepTest> :t x
> x :: forall a. a
> *DepTest> x
> getTcTyVar a {- tv aXJ -}
> getTcTyVar a {- tv aXJ -}
> getTcTyVar a {- tv aXJ -}
> getT
On Wed, Apr 14, 2004 at 04:58:55PM +0100, Keith Wansbrough wrote:
> > data Show' = forall a . Show a => Show' a
>
> The "forall a. Show a =>" context here has no effect on the
> representation; it merely constrains applications of the data
> constructor Show'. Since you have to say
>
> > print
> data Show' = forall a . Show a => Show' a
The "forall a. Show a =>" context here has no effect on the
representation; it merely constrains applications of the data
constructor Show'. Since you have to say
> print' :: Show' -> IO ()
anyway (thus providing the dictionary) there is no point in
Hello all-
I'm still playing with simulating dependent types using rank-2
polymorphism, and I've run into a small stumbling block on unwrapping
existential datatypes: they can't be let-bound (monomorphic
restriction?), but can be unwrapped in a case or lambda. Actually, I
find that assignment
I am pleased to announce the HSQL library version
1.4. The HSQL is a simple library, which provides
interface to multiple databases. MySQL, PostgreSQL,
ODBC and SQLite are currently supported.
What is new?
1. The ODBC interface provides the "driverConnect"
function which is an al
A new version of Happy, the parser generator for Haskell, has been
released. Version 1.14 is a small increment relative to 1.13, whose
purpose is mainly to introduce one new feature which will be reuqired to
compile future versions of GHC.
>From the release notes:
* New meta-veriable $>
Dear Haskellers,
two changes of season and one of editor later, we strongly suspect
the Haskell community has also moved along admirably. Thus comes
the need to refresh our list of all things Haskell, and give *you*
the opportunity to tell all the world about your passion.
We invite your contribu
In thinking about a data storage model for a web
app I wanted to develop, and in finding Haskell so
concise and expressive, I wondered if one could
write a relational DBMS in Haskell in under 1000
lines of code. The answer appears to be yes!
Features:
* non-destructive-update Haskell DBMS (can us
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