[Haskell-cafe] ANN: bimap 0.1 - a bidirectional map

[Neil Mitchell]

Hi Stuart,

> Data.Bimap is a data structure that represents a bidirectional mapping
> between two key types. A bimap has two type parameters; each value in
> the bimap is associated with exactly one value of the opposite type.
> In other words, it's a bijection between (subsets of) its argument
> types.

Very  handy, I actually wanted something similar myself a few days ago
and came up with:

http://www.cs.york.ac.uk/fp/darcs/firstify/Yhc/Core/Firstify/Mitchell/BiMap.hs

A few design differences from your one:

* I called my module BiMap" rather than "Bimap" - I debated this with
a collegue, and we settled on the capital M, but it was a very close
call.

* I have no L/R and Either variants. I decided it was better to be a
superset of Data.Map, and then have lookupRev/memberRev functions for
the R versions. Do you think anyone is likely to use the Either
variant, without a constant Left or Right in the code? Is this an
artefact of how its easier to code, rather than to use?

* I didn't push my Bimap to completion, because I am too lazy, and
hoped others would. Only the methods I needed were implemented. Many
thanks for doing this work!

Thanks

Neil