While hacking around with MPCs, trying to define a variant of the
Collection class, mutated to suit my own fiendish ends, I ran into
this:
Intervals.hs:345:
Class type variable `e' does not appear in method signature
union2 :: s -> s -> s
What's the significance of this restriction? (I presume this is caused
by a requirement that all class vars appear in all methods.) I don't
recall it being mentioned in the proposal for MPCs, but I may have
overlooked and/or forgotten it. I don't suppose it ever really "bites"
anyone, since one can always shove the appropriate constraint on the
missing variable into the other methods, that do use it, but I don't
instantly see why that's The Way to do it.
Slainte,
Alex.
