On Sun, 19 Oct 2014, Michael Snoyman wrote:
Overall, the problem is that we've overloaded Show in (at least) three different ways:
* Textual serialization * Debugging * User-friendly display of data
Unfortunately, the Show class is not used consistently, with the different uses you have listed. The automatically derived Show instances show valid Haskell expressions, that you can enter into GHCi in order to get back the shown value. I think we should stick to that meaning. Strictly conforming to this rule would also mean that using 'show' for formatting numbers is not precisely correct, because we cannot expect that other tools can parse all ways of writing number literals in Haskell. Maybe printf is better here, but it is unfortunately not total. Following the above rule for functions would mean, that 'show' should emit an expression that represents the function, e.g. something like Prelude> show ((\x->x*x) :: Int -> Int) fromJust . flip lookup [(0,0), (1,1), (-1,1), (2,4), (-2,4), ...