Proposal: Add Eq instance for Control.Exception.ErrorCall

Simon Hengel sol at
Tue Nov 27 11:59:05 CET 2012

I propose to add an Eq instance for ErrorCall.  The main motivation is
to make it more convenient to construct predicates that select specific

My current use case is testing for expected exceptions.  In Hspec[1] we
use predicates for that, e.g.:

  evaluate (head []) `shouldThrow` (== ErrorCall "Prelude.head: empty list")

But I think it can be useful in other situations and it is consistent
with the fact that other common exception types have an Eq instance
(e.g. ArithException, IOException, ExitCode).

Discussion period: 3 Weeks



More information about the Libraries mailing list