/// <summary>
/// Memoize the result
/// </summary>
public static Func <EitherPair <L, R> > Memo <L, R>(this Either <L, R> self)
{
var res = self();
return(() => res);
}
/// <summary>
/// Get the Left value
/// NOTE: This throws an InvalidOperationException if the object is in the
/// Right state
/// </summary>
public static bool IsLeft <L, R>(this Either <L, R> m)
{
return(m().IsLeft);
}
/// <summary>
/// Monadic append
/// If the left-hand side or right-hand side are in a Left state, then Left propagates
/// </summary>
public static Either <L, R> Mappend <L, R>(this Either <L, R> lhs, Either <L, R> rhs)
{
if (rhs == null)
{
throw new ArgumentNullException("rhs");
}
return(() =>
{
var lhsV = lhs();
if (lhsV.IsLeft)
{
return lhsV;
}
else
{
var rhsV = rhs();
if (rhsV.IsLeft)
{
return rhsV;
}
else
{
if (lhsV.Right is IAppendable <R> )
{
var lhsApp = lhsV.Right as IAppendable <R>;
return new EitherPair <L, R>(lhsApp.Append(rhsV.Right));
}
else
{
// TODO: Consider replacing this with a static Reflection.Emit which does this job efficiently.
switch (typeof(R).ToString())
{
case "System.Int64":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToInt64(lhsV.Right) + Convert.ToInt64(rhsV.Right)), typeof(R)));
case "System.UInt64":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToUInt64(lhsV.Right) + Convert.ToUInt64(rhsV.Right)), typeof(R)));
case "System.Int32":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToInt32(lhsV.Right) + Convert.ToInt32(rhsV.Right)), typeof(R)));
case "System.UInt32":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToUInt32(lhsV.Right) + Convert.ToUInt32(rhsV.Right)), typeof(R)));
case "System.Int16":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToInt16(lhsV.Right) + Convert.ToInt16(rhsV.Right)), typeof(R)));
case "System.UInt16":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToUInt16(lhsV.Right) + Convert.ToUInt16(rhsV.Right)), typeof(R)));
case "System.Decimal":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToDecimal(lhsV.Right) + Convert.ToDecimal(rhsV.Right)), typeof(R)));
case "System.Double":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToDouble(lhsV.Right) + Convert.ToDouble(rhsV.Right)), typeof(R)));
case "System.Single":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToSingle(lhsV.Right) + Convert.ToSingle(rhsV.Right)), typeof(R)));
case "System.Char":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToChar(lhsV.Right) + Convert.ToChar(rhsV.Right)), typeof(R)));
case "System.Byte":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToByte(lhsV.Right) + Convert.ToByte(rhsV.Right)), typeof(R)));
case "System.String":
return new EitherPair <L, R>((R)Convert.ChangeType((Convert.ToString(lhsV.Right) + Convert.ToString(rhsV.Right)), typeof(R)));
default:
throw new InvalidOperationException("Type " + typeof(R).Name + " is not appendable. Consider implementing the IAppendable interface.");
}
}
}
}
});
}
/// <summary>
/// Returns true if the monad object is in the Right state
/// </summary>
public static bool IsRight <L, R>(this Either <L, R> m)
{
return(m().IsRight);
}
