Proposal: Extensible exceptions

Yitzchak Gale gale at
Fri Jul 4 10:54:11 EDT 2008

Ian Lynagh wrote:
> This is a proposal to replace the current exception mechanism in the
> base library with extensible exceptions...

How does this affect integration between IO exceptions
and pure exceptions, in particular Control.Monad.Error from mtl?

That is already a bit tricky, but doable. Does this make it

At the very least, we should take this opportunity to create
Error instances for the standard exceptions, and make sure
that the extension mechanism includes an easy way to
add compatible Error instances for new exceptions.

Besides the mechanism itself, the obvious question is
how to do this without making a mess out of the package
dependency hierarchy.


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