public static Writer <Out, Reader <E, V> > SelectMany <Out, E, T, U, V>(
this Writer <Out, T> self,
Func <T, Reader <E, U> > bind,
Func <T, U, V> project
)
{
if (bind == null)
{
throw new ArgumentNullException(nameof(bind));
}
if (project == null)
{
throw new ArgumentNullException(nameof(project));
}
return(() =>
{
var resT = self.Valid()();
if (resT.IsBottom)
{
return WriterResult.Bottom <Out, Reader <E, V> >(resT.Output);
}
return WriterResult.Return <Out, Reader <E, V> >(env =>
{
var resU = bind(resT.Value).Valid()(env);
if (resU.IsBottom)
{
return ReaderResult.Bottom <V>();
}
return ReaderResult.Return(project(resT.Value, resU.Value));
}, resT.Output);
});
}
internal static Reader <Env, T> Valid <Env, T>(this Reader <Env, T> self) => self ?? (_ => ReaderResult.Bottom <T>());
private static ReaderResult <T> Bottom <T>() => ReaderResult.Bottom <T>();