Use a combinator in place of a function

--HG--
extra : amend_source : 00481b425021a6356f51a8ca6ccfe3e17e9a23f6
Merge
Simplify t_mapEitherWithKey
Redo t_mapMaybeWithKey to check against a reference implementation
Start a little test abstraction with a roundtrip function

--HG--
extra : histedit_source : 589745973c198796525fb3ae94b98402c1368e71%2C4b68108453af817db7f312995e86efb03752944d
More simplifications via use of roundtrip

--HG--
extra : amend_source : 8589048c29726fc6b9c02f8ffd99c63b9fdf8e84
extra : histedit_source : 0368530e0d6098d19d761fe557a597f7a519caf5
Simplify t_findMin and t_findMax

--HG--
extra : histedit_source : 12a000fdb3d4de771c3f7c9caf633920182a8714
Extract roundtrip into roundtrip0

--HG--
extra : amend_source : f4d406292850beec538025f0d57fd1ea4bc44c2f
extra : histedit_source : d335b335cf8aa07cbc450e926afbd79c7767ed0f
Generalize the type of roundtrip a little
More simplifications via roundtrip and roundtrip0

--HG--
extra : amend_source : 9988f758a9dc06b06503d43a61b4148eb137925c
extra : histedit_source : 84532ff1ca694dbd2da56a7f2d304a879f141973%2C6770c5fa7972751450124d76a01820ef2be1df2a
Rename roundtrip0 to isoWith

The name is intended to be reminiscent of "isomorphic with".

--HG--
extra : amend_source : 13d0af1e95b45b2b6596f66a4f0c22a0b04bfd42
extra : histedit_source : d0322a0ab8f5517fcb6d4528fa549c59d7409a07
Rename roundtrip to (===)

--HG--
extra : amend_source : b2b63a70ca4fa9f2afc7e2b658373ec0e36fcd1c
Merge