public static Nullable <TResult> SelectMany <TSource, TNullable, TResult>(
this Nullable <TSource> source,
Func <TSource, Nullable <TNullable> > projector,
Func <TSource, TNullable, TResult> selector)
where TSource : struct
where TResult : struct
where TNullable : struct
{
return(source
.Bind(s => projector(s).Bind(value => Unit(selector(s, value)))));
}
public static Nullable <char> Nullable_MoreComposition()
{
string sentence = "Hello world!";
Nullable <char> charToFind = NullableMonad.Unit('H');
Nullable <char> nextChar = charToFind
.Bind(chr => GetIndexOfCharacter(sentence, chr))
.Bind(index => GetCharacterAtIndex(sentence, index + 1));
return(nextChar);
}
public void Bind()
{
Nullable <int> n = 2;
Nullable <int> n0 = null;
Assert.Throws <ArgumentNullException>(() => NullableExtensions.Bind <int, int>(n, null));
Func <int, int?> binder1 = i => i * 2;
Func <int, int?> binder2 = _ => null;
Assert.True(n.Bind(binder1).HasValue);
Assert.Equal(4, n.Bind(binder1).Value);
Assert.False(n0.Bind(binder1).HasValue);
Assert.False(n.Bind(binder2).HasValue);
Assert.False(n0.Bind(binder2).HasValue);
// selector not called
Assert.False(n0.Bind(new Func <int, int?>(_ => throw new InvalidOperationException("Should not be called"))).HasValue);
}
