flatMap<R, A, B> function
flatMap transforms the previous computation result using the given function.
Implementation
ReaderTask<R, B> Function(ReaderTask<R, A>) flatMap<R, A, B>(
ReaderTask<R, B> Function(A a) f,
) =>
(fa) => ReaderTask((r) => fa(r).chain(T.flatMap((a) => f(a)(r))));