Re: [Haskell-cafe] Questions about the Functor class and it's use in "Data types à la carte"

jerzy.karczmarczuk@info.unicaen.fr wrote:

Roberto Zunino writes:

...

without seq, there is no way to distinguish between undefined and (const undefined),

"no way to distinguish" is perhaps too strong. They have slightly different types.

At a particular type which they both inhabit, such as (a->b) or, to be concrete, (Int -> Int), there is no way to distinguish without seq. Jules