retreat from using type classes for SPDs

see also: http://stackoverflow.com/questions/16101284/polymorphic-return-type-interfaces-callbacks
retreat from using type classes for Shapes

see also: http://stackoverflow.com/questions/16101284/polymorphic-return-type-interfaces-callbacks
retreat from using type classes for Primitives

see also: http://stackoverflow.com/questions/16101284/polymorphic-return-type-interfaces-callbacks