errorM and errorIO

[gregwebs]

for consistency, error should be change to use Text. Often times though, error is used out of convenience in IO when one is not supposed to be using it.

errorIO :: (MonadBase IO m) => Text-> m a
errorIO = throwIO . userError . unpack

errorM would use throwM. I would like to push this upstream, but I don't think there is any upstream that depends on Text.

[snoyberg]

I'm a solid +1 on adding errorM and errorIO. I'm less certain of switching to Text. While I agree with you that this would be more consistent, I have a nagging worry that this will cause too much breakage. The reasons I left it as String in the first place were (1) there's no performance advantage, since we'll need to unpack to String anyway, and (2) a number of libraries hardcode their error outputs as String (I think attoparsec does this, for instance).

Anyway, I'm not opposed necessarily, just airing my concerns.

[gregwebs]

Agreed this is not about performance. I find myself always using Text. But I can change it in my application