Proposal: Add Eq instance for Control.Exception.ErrorCall

Henning Thielemann lemming at
Tue Nov 27 14:07:21 CET 2012

On Tue, 27 Nov 2012, Simon Hengel wrote:

> If the function/value under specification is so "insane" that it
> contains a /set of exceptions/, then you have to be prepared to get any
> of those [1]:
>  evaluate value
>    `shouldThrow` (||) <$> (== ErrorCall "foo") <*> (== ErrorCall "bar")
> Again, I'm not implying that it's a good idea to write a function that
> behave like that.  But if you do, I'd at least like to have it
> documented ;)

My advice to programmers is: If you are starting to document insane 
behavior, wait a minute and think about how to avoid it. In many cases 
this helps. :-) Having said that you might assist the users of hspec by 
providing variants of shouldThrow, say shouldCallError, that matches error 
messages. Additionally I would add a DEPRECATE pragma to shouldCallError 
with a message that tells the programmer that he should think twice.

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