Hi there,
I'm currently writing an interpreter that I would like to be able to
use with other haskell programs. I would like to be able to pass along
arbitrary types though the interpreter. I've seen hints that GADTs can
do this, but I am having trouble understanding them.
So far, I've learnt
Hey Kev,
The types are thrown away during compile time. Therefore, if you
have a constructor VWrapper :: a - Value nothing is known about
that a when you scrutinize it.
What you could do, however, is something like this:
data Value a where
VInt :: Integer - Value Integer
...
Then you could add a specific constructor for String. The main point
is: the case construct only works for values, not for types. There is
no typecase construct. If you want to have certain restrictions on the
'a', such as the Show class, you could also do something like this:
data Value
Oops, wrong mail account for my last email. Apologies.
What I'm trying to accomplish is being able to write haskell libraries
for the interpreter that don't use the interpreter's predefined Value
types, without having to edit the Value type itself and add a new
constructor (i.e. it's abstracted
On Mon, Jul 13, 2009 at 12:41 PM, Kev
Mahoneymaill...@kevinmahoney.co.uk wrote:
So far, I've learnt you can do this:
data Value where
VInt :: Integer - Value
...
VWrapper :: a - Value
which can let you encode arbitrary 'dynamic' types into Value. I was
hoping to be able to pattern match
Thanks, I hadn't noticed Data.Dynamic. It never even occurred to me
that something like this would be in the standard libraries. It looks
like it's precisely what I was looking for, after a brief scan of the
documentation.
I will report back if I bump into any problems with it
2009/7/13 Chaddaï
On Mon, Jul 13, 2009 at 9:18 AM, Kev Mahoneymaill...@kevinmahoney.co.uk wrote:
That said, I think I may defer this until I understand the ins and
outs of Haskell's type system a little better. I think a parametrized
type will be the only way to do it. The only reason I thought GADTs
may be
On Mon, Jul 13, 2009 at 6:09 AM, Chris Eidhof ch...@eidhof.nl wrote:
Hey Kev,
The types are thrown away during compile time. Therefore, if you have a
constructor VWrapper :: a - Value nothing is known about that a when
you scrutinize it.
What you could do, however, is something like this:
