public void NestedBacktracking()
{
var tokens = new List <Token>
{
new IdentifierToken("x"),
new SymbolToken(SymbolType.Equals),
new IdentifierToken("3")
};
var enumerator = new TokenEnumerator(tokens.ToArray());
Assert.AreEqual(new IdentifierToken("x"), enumerator.Current);
Assert.AreEqual(true, enumerator.MoveNext());
enumerator.SetBacktrackPoint();
Assert.AreEqual(new SymbolToken(SymbolType.Equals), enumerator.Current);
Assert.AreEqual(true, enumerator.MoveNext());
enumerator.SetBacktrackPoint();
Assert.AreEqual(new IdentifierToken("3"), enumerator.Current);
Assert.AreEqual(false, enumerator.MoveNext());
enumerator.Backtrack();
Assert.AreEqual(new IdentifierToken("3"), enumerator.Current);
Assert.AreEqual(false, enumerator.MoveNext());
enumerator.Backtrack();
Assert.AreEqual(new SymbolToken(SymbolType.Equals), enumerator.Current);
Assert.AreEqual(true, enumerator.MoveNext());
Assert.AreEqual(new IdentifierToken("3"), enumerator.Current);
Assert.AreEqual(false, enumerator.MoveNext());
Assert.AreEqual(null, enumerator.Current);
}
private T ParseWith <T>(params Func <T>[] methods)
where T : class
{
foreach (var method in methods)
{
tokens.SetBacktrackPoint();
T result = method();
if (!(result is null))
{
return(result);
}
tokens.Backtrack();
}
return(null);
}