[Haskell-beginners] Confused by type constraints

[Brandon Allbery]

On Fri, Jun 3, 2011 at 09:55, Daniel Schoepe
<daniel.schoepe at googlemail.com> wrote:
> The constraints in the data type declaration only affect the
> constructors. It's a known issue, unfortunately there doesn't seem to be
> a way around it.

GADTs handle it as expected.  The core problem is with how the Haskell
98 standard declared them to work; the Haskell standards committee has
proposed removing them altogether from non-GADT syntax since they're
worse than useless as is.