Dear Cafe,

in containers, we have Data.IntMap/IntSet .
Because of the underlying implementation (patricia trees),
keys/elements indeed have to be Int (we need their bits).

This is a conflict with type-safety: I try to avoid Int,
and use some  newtype T = T Int  instead.
E.g., I want to distinguish several different indices
for the same structure, like row and column numbers
in (sparse) matrices, or vertices in bipartite graphs.

So, I made these trivial wrappers EnumMap and EnumSet:
https://github.com/jwaldmann/satchmo-solver/tree/master/src/Data

Is this reasonable (do from/toEnum really have zero cost)?
Would this be a useful addition to containers?

- J.W.


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