Re: [Haskell-cafe] Learn You a Haskell for Great Good - a few doubts

On 7 Mar 2011, at 23:38, Alexander Solla wrote:

_|_ /= (_|_,_|_)

...

(undefined, undefined) (*** Exception: Prelude.undefined

That is as close to Haskell-equality as you can get for a proto-value that does not have an Eq instance. As a consequence of referential transparency, evaluation induces an equivalence relation. This implies that (_|_, _|_) = _|_ = (_|_, _|_).

Surely the key thing is the '(' character which is produced immediately before the exception is encountered. I'd say that demonstrates that in GHC _|_ /= (_|_,_|_). --Ben