Additions to Control.Exception: withException, displaySomeExceptionType

Requires RankNTypes though.

-- | Apply a function to whatever @Exception@ type is inside a
-- @SomeException@.
withException :: forall r. (forall e. Exception e => e -> r) -> SomeException -> r
withException f (SomeException e) = f e

-- | Use 'withException' to obtain the exception's type name.
displaySomeExceptionType :: SomeException -> String
displaySomeExceptionType = withException (show . typeOf)

Trac metadata

Trac field	Value
Version	8.6.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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changed weight to 5

added Tfeature request Trac import core libraries labels

added Pnormal label

I am +1 on these. @core-libraries ?

+1 to the first, with a question for the second. Should

displaySomeExceptionType :: SomeException -> String
displaySomeExceptionType = withException (show . typeOf)

just be this?

displaySomeExceptionType :: SomeException -> String
displaySomeExceptionType = withException displayException

Besides not meeting the Fairbarn threshold for me, I don't quite understand the incentive for displaying an exception type as opposed to its specified representation. Thoughts?

Revision to my opinion:

I am only +1 on the first. I'm out on the second, unless you can provide sufficient argument for its inclusion (I don't think it will be that useful in practise)