Discussion: adding displayException to Exception class

[John Lato]

On Wed, Oct 29, 2014 at 10:33 AM, Michael Snoyman <michael at snoyman.com>
wrote:

>
> A completely different approach that might be better for your use case
> *and* might be useful in other cases would be to keep a stack of the
> `TypeRep`s we converted through when creating the SomeException. However,
> that would require a breaking change to SomeException, which I really
> *don't* want to propose.
>

We already keep all the TypeReps, they just aren't generically accessible.
If we added a function to the Exception class like

  typeRepStack :: a -> [TypeRep]

it should work.  A more-or-less sensible default is typeRepStack a =
[typeOf a], which would work for all terminal exception types.  A mid-level
type in a hierarchy would need a different value though, something like

   typeRepStack se@(SomeException e) = typeOf se : typeRepStack e
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