static <A, B> Equal<Writer<A,B>>
writerEqual(Equal<A> eq1, Equal<B> eq2)
<B> Writer<W,B>
flatMap(F<A,Writer<W,B>> f)
map(F<A,B> f)
Writer<W,A>
tell(W w)
static <W, A> Writer<W,A>
unit(A a, Monoid<W> m)
unit(A a, W w, Monoid<W> m)
static <B> Writer<String,B>
unit(B b)
static <A> F<A,Writer<String,A>>
stringLogger()