29 Oct
2018
29 Oct
'18
4:28 p.m.
Paterson, Ross wrote:
I think that fail on Either or EitherT has always been the default (error).
By "old" I meant "really old". The instance was changed 8 years ago, when ghc-7.0.1 was released. You can find traces of it in Control.Monad.Error in mtl-1.*. mtl-2.* removed those traces. The last appearance was in mtl-1.1.1.1, conditional on the version of base: https://hackage.haskell.org/package/mtl-1.1.1.1/docs/src/Control-Monad-Error... Further back in history, mtl-1.0.0 was released with ghc-6.4.1, and contained the above instance unconditionally; before that, the instance was in base. I stopped looking at ghc-6.0.1. Cheers, Bertram