Am 26.02.2014 14:19, schrieb Christian Maeder:
Hi,
I tend to agree to this proposal, but I would like to encourage developers/researchers to invent something like named instances (or dictionaries), that are not transitively reexported and could coexist with current instances. (These would allow several, differently named, instances for the same type and class combination.)
I expressed the idea of programmable instance selection in the past: http://www.haskell.org/pipermail/libraries/2013-March/019533.html http://www.haskell.org/pipermail/libraries/2012-November/018831.html This approach may also solve the orphan instance problem, but I have no idea how to design programmable instance selection. However, I suspect that GHC assumes at several places that there is only one instance per pair of class and type. What about packing and unpacking of class dictionaries in existentially quantified types?