code: public <T,R> Higher<CRE,Higher<C2,R>> map(Function<? super T,? extends R> fn, Higher<CRE,Higher<C2,T>> ds){
         return f.map(h->g.map(fn,h) ,ds);
      }
docs: Transformation operation
  
  @param fn Transformation function
  @param ds Datastructure to transform
  @return Transformed data structure