Re: [Haskell-cafe] Why Either = Left | Right instead of something like Result = Success | Failure

On May 27, 2010, at 10:53 , Vo Minh Thu wrote:

2010/5/27 Ionut G. Stan :

...

I was just wondering if there's any particular reason for which the two constructors of the Either data type are named Left and Right. I'm thinking that something like Success | Failure or Right | Wrong would have been a little better.

I've recently seen that Scala uses a similar convention for some error notifications so I'm starting to believe there's more background behind it than just an unfortunate naming.

Either *can* be used to represent success and failures, but not necessarily. It is a convention, when using Either to model success/failure, to use Right for success and Left for failure. Even if Left as a word does not match with the meaning of failure, it is easy to get it Right :)

Historically it *has* been related to negativity in many cultures. (Consider "sinister", cognate of Italian "sinistro/a", and the prevalence of and preference for right-handed-ness.) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH