> At present we can easily express different flavors of conjunction, but
> expressing disjunction is hard.
Disjunction is not particularly difficult. See, for example,
http://okmij.org/ftp/Haskell/TTypeable/TTypeable.hs
and search for ORELSE. The code demonstrates higher-order type-level
programming (for example, higher-order function Member with
the equality predicate as the argument). The file implements
closed-world negation for type predicates. See
http://okmij.org/ftp/Haskell/typeEQ.html
for explanations.
Incidentally, one application of that machinery is precisely your
original problem. The code
http://okmij.org/ftp/Haskell/TTypeable/NotAFunctionT.hs
implements vector spaces as function spaces, so you can use the same
operation <+> :: Vspace v => v -> v -> v to add arguments of the type
(Num n =>n), Num n => a -> n, Num n => a -> b -> n, etc.
(there is also a scalar-vector multiplication).
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