// Monad
public static IMaybe <TResult> SelectMany <T, TResult>(
this IMaybe <T> source,
Func <T, IMaybe <TResult> > selector)
{
return(source.Accept(
new SelectManyMaybeVisitor <T, TResult>(selector)));
}
public void SimpleQueryExpressionWorks()
{
IMaybe <int> sut = new Just <int>(42);
IMaybe <string> actual = from i in sut
select i.ToString();
Assert.Equal(
"42",
actual.Accept(new FromMaybeVisitor <string>("nothing")));
}
public static T GetValueOrDefault <T>(this IMaybe <T> source, T defaultValue)
{
return(source.Accept(new FromMaybeVisitor <T>(defaultValue)));
}
public static bool IsNothing <T>(this IMaybe <T> source)
{
return(source.Accept(new IsNothingVisitor <T>()));
}
// Monad
public static IMaybe <T> Flatten <T>(this IMaybe <IMaybe <T> > source)
{
return(source.Accept(new FlattenMaybeVisitor <T>()));
}
public static IChurchBoolean IsJust <T>(this IMaybe <T> m)
{
return(m.Accept(new IsJustMaybeVisitor <T>()));
}