My point is that you can't override what equality implementation groupByToMap will use, which makes it much less useful. See for example https://gcanti.github.

My point is that you can't override what equality implementation groupByToMap will use, which makes it much less useful. See for example https://gcanti.github.io/fp-ts/modules/NonEmptyArray.ts.html#group https://gcanti.github.io/fp-ts/modules/NonEmptyArray.ts.html..., where you can supply your own equality function…