/// <summary>
/// Creates a new FA that matches the specified FA expression or empty
/// </summary>
/// <param name="expr">The expression to make optional</param>
/// <param name="accept">The symbol to accept</param>
/// <returns>A new FA that will match the specified expression or empty</returns>
public static CharFA <TAccept> Optional(CharFA <TAccept> expr, TAccept accept = default(TAccept))
{
var result = expr.Clone();
var f = result.FirstAcceptingState;
f.AcceptSymbol = accept;
result.EpsilonTransitions.Add(f);
return(result);
}
/// <summary>
/// Creates a new FA that will match a repetition of the specified FA expression
/// </summary>
/// <param name="expr">The expression to repeat</param>
/// <param name="minOccurs">The minimum number of times to repeat or -1 for unspecified (0)</param>
/// <param name="maxOccurs">The maximum number of times to repeat or -1 for unspecified (unbounded)</param>
/// <param name="accept">The symbol to accept</param>
/// <returns>A new FA that matches the specified FA one or more times</returns>
public static CharFA <TAccept> Repeat(CharFA <TAccept> expr, int minOccurs = -1, int maxOccurs = -1, TAccept accept = default(TAccept))
{
expr = expr.Clone();
if (minOccurs > 0 && maxOccurs > 0 && minOccurs > maxOccurs)
{
throw new ArgumentOutOfRangeException(nameof(maxOccurs));
}
switch (minOccurs)
{
case -1:
case 0:
switch (maxOccurs)
{
case -1:
case 0:
var result = new CharFA <TAccept>();
var final = new CharFA <TAccept>(true, accept);
final.EpsilonTransitions.Add(result);
foreach (var afa in expr.FillAccepting())
{
afa.IsAccepting = false;
afa.EpsilonTransitions.Add(final);
}
result.EpsilonTransitions.Add(expr);
result.EpsilonTransitions.Add(final);
return(result);
case 1:
return(Optional(expr, accept));
default:
var l = new List <CharFA <TAccept> >();
expr = Optional(expr);
l.Add(expr);
for (int i = 1; i < maxOccurs; ++i)
{
l.Add(expr.Clone());
}
return(Concat(l, accept));
}
case 1:
switch (maxOccurs)
{
case -1:
case 0:
var result = new CharFA <TAccept>();
var final = new CharFA <TAccept>(true, accept);
final.EpsilonTransitions.Add(result);
foreach (var afa in expr.FillAccepting())
{
afa.IsAccepting = false;
afa.EpsilonTransitions.Add(final);
}
result.EpsilonTransitions.Add(expr);
return(result);
case 1:
return(expr);
default:
return(Concat(new CharFA <TAccept>[] { expr, Repeat(expr.Clone(), 0, maxOccurs - 1) }, accept));
}
default:
switch (maxOccurs)
{
case -1:
case 0:
return(Concat(new CharFA <TAccept>[] { Repeat(expr, minOccurs, minOccurs, accept), Repeat(expr, 0, 0, accept) }, accept));
case 1:
throw new ArgumentOutOfRangeException(nameof(maxOccurs));
default:
if (minOccurs == maxOccurs)
{
var l = new List <CharFA <TAccept> >();
l.Add(expr);
for (int i = 1; i < minOccurs; ++i)
{
l.Add(expr.Clone());
}
return(Concat(l, accept));
}
return(Concat(new CharFA <TAccept>[] { Repeat(expr.Clone(), minOccurs, minOccurs, accept), Repeat(Optional(expr.Clone()), maxOccurs - minOccurs, maxOccurs - minOccurs, accept) }, accept));
}
}
// should never get here
throw new NotImplementedException();
}
