Christian Maeder wrote:
Agreed, but suppose you have Symbols with their positions. Then you may like that a set of symbols is printed with the positions last (or first) inserted, although positions are ignored in camparisons.
C.
It seems that there are two uses of Set e: 1) the Ord-comparison of e's is a total ordering / Eq e implements semantic equality; 2) Eq e is some equivalence relation, such as in Christian's example above. I agree with Jean-Philippe that 2) must not be advocated: users should always use a Map instead (e.g. Map Symbol Position, with 'real equality' on Symbol). Now, it may save effort to *implement* Map by doing exactly 2), with e = MapElement a b. The work needed to reimplement Map would have to be compared to the work needed to ensure that Set supports use 2). However, this is purely a consideration of implementation, and does not effect the user experience of Set and Map - provided that she only uses Set as per 1). Greetings, Arie