Actually, IIRC, _|_ is actually a member of _all_ types.
--ag
"S. Alexander Jacobson" wrote:
>
> On Tue, 28 Sep 1999, Adrian Hey wrote:
>
> > So (a && b) = (b && a) is invalid
>
> && has type
> &&::Boolean->Boolean->Boolean
>
> _|_ is not of type Boolean. So, if you pass && a value of type _|_,
> you have violated its type requirements (precondition) and should not
> expect expect a lawful result.
>
> Haskell's type checker is not able to prevent you from passing _|_ to &&.
> I don't think this failure makes Haskell not a functional language (all
> functions have preconditions!).
> I do think it makes Haskel less than perfectly type-safe.
>
> I believe that Charity disallows _|_. I don't know whether the cost of
> doing so is worth the gain in type safety.
>
> -Alex-
>
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