ambiguous_method.m:022: In declaration for function `e'/0:
ambiguous_method.m:022:   error in type class constraints: type variable `E'
ambiguous_method.m:022:   occurs in the constraints, but is not determined by
ambiguous_method.m:022:   the function's argument or result types.
ambiguous_method.m:022:   All types occurring in typeclass constraints must be
ambiguous_method.m:022:   fully determined. A type is fully determined if one
ambiguous_method.m:022:   of the following holds:
ambiguous_method.m:022:   1) All type variables occurring in the type are
ambiguous_method.m:022:   determined.
ambiguous_method.m:022:   2) The type occurs in a constraint argument, that
ambiguous_method.m:022:   argument is in the range of some functional
ambiguous_method.m:022:   dependency for that class, and the types in all of
ambiguous_method.m:022:   the domain arguments for that functional dependency
ambiguous_method.m:022:   are fully determined.
ambiguous_method.m:022:   A type variable is determined if one of the following
ambiguous_method.m:022:   holds:
ambiguous_method.m:022:   1) The type variable occurs in the argument types of
ambiguous_method.m:022:   the predicate, function, or constructor which is
ambiguous_method.m:022:   constrained.
ambiguous_method.m:022:   2) The type variable occurs in a type which is fully
ambiguous_method.m:022:   determined.
ambiguous_method.m:022:   See the "Functional dependencies" section of the
ambiguous_method.m:022:   reference manual for details.