[Haskell-cafe] The applicative instances for Either?

Ketil Malde ketil at malde.org
Sat Sep 17 08:42:42 CEST 2011


I have a program that makes use of the applicative instance for Either
String.  I used to define these instances locally, but at some point,
they became part of Control.Applicative.  I have limited the
dependencies to 'base >= 4', but apparently, some version 4s of base
include this instance, some do not, and it causes problems for people
trying to compile the program.

Is there any information, or otherwise accessible source specifying
exactly when this was changed, so that I can have more precise
dependencies?  And is there a simple way to handle this conditionally,
either within cabal, or using CPP?

If I haven't seen further, it is by standing in the footprints of giants

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