Tomasz Zielonka wrote:
On 9/27/07, [EMAIL PROTECTED]
<[EMAIL PROTECTED]> wrote:
Thomas Conway writes:
On 9/27/07, ok <[EMAIL PROTECTED]> wrote:
I have often found myself wishing for a small extension to the syntax of
Haskell 'data' declarations. It goes like this:
['where' clause to allow locally defined names in type declarations]
Nice.
Quite a few times I've found myself declaring type synonyms for this
reason, but you end up polluting the global namespace.
+1 vote.
Data with where?
You haven't heard about GADTs?
I think that you haven't read the question carefully, because "where"
in GADTs is simply a syntactic sugar. However, this seems to be
available already with GADTs and type equality constraints:
data BST key val where
Empty :: BST key val
Fork :: (bst ~ BST key val) => key -> val -> bst -> bst -> BST key val
It's a pity you can't use bst (or a type synonym) instead of the last
"BST key val".
Indeed. GADT syntax looks like a type signature (except for strictness
annotations, which presently aren't part of function syntax!) but
apparently the (->)s and result-type aren't type-signature, because
type-synonyms can't be used for them. I tried. (because there were
several GADT constructors with slightly different signatures, so I made
a type-synonym with an argument to try to shorten them). It seems a
pity to me too.
Isaac
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
