1. Add a new method to the Exception typeclass:
-- | Render this exception value in a human-friendly manner. Default implementation: @show@. displayException :: e -> String displayException = show
I'm +0.5 on this one, even though I think we should solve this in the general case. I think there is a difference between converting something to a string (display) vs. showing something in a programmer friendly way (show). This distinction is not novel, both Python and Ruby make that distinction (str()/repr() in Python, #to_s/#inspect in Ruby). So I would love to have tho following type class: class Display a where display :: a -> String default display :: Show a => a -> String display = show Note that for many Prelude types `show == display`, with the notable exception of String, where `display = id`. One use case where this matters is string interpolation [1][2][3]. Other programming language communities use `toString`, `str` and `to_s` for this primitive [4]. So maybe ToString/toString would be a better class/method name.
2. Modify GHC's default exception handler to use `displayException` instead of `show`.
I'm -1 on this one. From my perspective most of the time uncaught exceptions are encountered by programmers. So I would prefer to have the programmer friendly version by default. In cases where I want the "user friendly behavior" I'm ok with the extra step of adding a custom exception handler. Ideally, we would already provide a convenient way to do so. Cheers, Simon [1] http://hackage.haskell.org/package/interpolate [2] http://hackage.haskell.org/package/interpolatedstring-qq [3] http://hackage.haskell.org/package/interpolatedstring-perl6 [4] https://github.com/sol/exceptions-by-language