On Wed, Oct 29, 2014 at 10:39 AM, Herbert Valerio Riedel
Hi Michael,
On 2014-10-29 at 00:43:55 +0100, Michael Snoyman wrote:
I don't want to make a format proposal yet, just open up discussion on an issue, and see how others feel about it.
As I recently commented on this list[1], the Show typeclass is overloaded with multiple meanings (serialization, debug info, and user-friendly data display). The general consensus seems to be that the official semantics for Show should be for serialization (as paired up with Read).
[...]
I have a possible solution that I'd like to propose as a strawman: add a new method to the Exception typeclass:
displayException :: e -> String displayException = show
As we're having the general problem of 'Show' being abused for pretty-printing, why not rather standardise on a pretty-show/printing typeclass that would not be limited to Exceptions? What am I missing?
The downside to that is that it introduces a breaking change, whereas this proposal does not. If we *do* want to standardize on a pretty-printing typeclass, I think the right way forward (though somewhat painful) is: Release X: Introduce the pretty-printing typeclass, add displayException with default implementation of Show, do not otherwise change Exception. Release X+1: Add new typeclass as a superclass of Exception. Release X+2: Switch default implementation of displayException to the pretty-show. Release X+3: Remove Show as a superclass. Maybe some of those steps can be combined, I'm not certain. Michael