Do not depend on package `either`

[andreasabel]

I can't install tog since I cannot install either. Maybe it is a good idea not to depend on package either, see also https://github.com/ekmett/either/issues/17

cabal install either
Resolving dependencies...
In order, the following would be installed:
exceptions-0.6.1 (reinstall) changes: mtl-2.1.3.1 -> 2.2.1,
transformers-0.3.0.0 -> 0.4.1.0
transformers-compat-0.3.3.4 (new version)
contravariant-1.2 (reinstall) changes: transformers-0.3.0.0 -> 0.4.1.0,
transformers-compat-0.3.3.3 -> 0.3.3.4
distributive-0.4.4 (reinstall) changes: transformers-0.3.0.0 -> 0.4.1.0,
transformers-compat-0.3.3.3 -> 0.3.3.4
comonad-4.2.2 (reinstall) changes: transformers-0.3.0.0 -> 0.4.1.0,
transformers-compat-0.3.3.3 -> 0.3.3.4
semigroupoids-4.2 (reinstall) changes: transformers-0.3.0.0 -> 0.4.1.0
bifunctors-4.1.1.1 (latest: 4.2) (reinstall)
profunctors-4.3.2 (new version)
free-4.9 (reinstall) changes: mtl-2.1.3.1 -> 2.2.1, profunctors-4.2.0.1 ->
4.3.2, transformers-0.3.0.0 -> 0.4.1.0
either-4.3.2 (new package)
cabal: The following packages are likely to be broken by the reinstalls:
lens-4.6
lens-4.4.0.2
trifecta-1.5
idris-0.9.14.2
reducers-3.10.3
profunctors-4.2.0.1
keys-3.10.1
pointed-4.1
Use --force-reinstalls if you want to install anyway.

[bitonic]

So installing tog on a clean sandbox doesn't work? How is this different from the usual cabal hell?

[bitonic]

In any case, I only need Data.Either.Validation. Feel free to copy that module only in the tog source tree.

[andreasabel]

Seems to work in a clean sandbox.