private bool HasHigherPrecedence(LexicToken current, LexicToken prev)
{
int currentPrecedence = this.GetPrecedence(current);
int prevPrecedence = this.GetPrecedence(prev);
return(currentPrecedence > prevPrecedence || (current is PowerLexicToken));
}
private void EvaluateToken(LexicToken token, List <LexicToken> output, Stack <LexicToken> operators)
{
if (token is WhitespaceLexicToken || token is ArgumentSeparatorLexicToken)
{
return;
}
// if constant, factorial or variable add to output
if (token is ConstantLexicToken || token is FactorialLexicToken || token is VariableLexicToken)
{
output.Add(token);
return;
}
if (token is LeftParenLexicToken)
{
operators.Push(token);
return;
}
if (token is RightParenLexicToken)
{
LexicToken op;
while (operators.CanPop())
{
op = operators.Pop();
if (op is LeftParenLexicToken)
{
break;
}
output.Add(op);
}
return;
}
if (!operators.Any())
{
operators.Push(token);
return;
}
LexicToken prev = operators.Peek();
if (prev is LeftParenLexicToken || this.HasHigherPrecedence(token, prev))
{
operators.Push(token);
}
else
{
output.Add(operators.Pop());
operators.Push(token);
}
}
private void ValidateLexingOutput(IList <LexicToken> tokens)
{
if (tokens.Count < 2)
{
return;
}
LexicToken t1 = null;
LexicToken t2 = tokens[0];
for (int i = 1; i < tokens.Count; i++)
{
t1 = t2;
t2 = tokens[i];
if ((t1 is ConstantLexicToken || t1 is VariableLexicToken) && (t2 is VariableLexicToken || t2 is FunctionLexicToken || t2 is LeftParenLexicToken))
{
tokens.Insert(i++, new MultiplyLexicToken());
}
}
}
private int GetPrecedence(LexicToken token)
{
if (token is AddLexicToken)
{
return(OperationPriorities.Addition);
}
else if (token is SubtractLexicToken)
{
return(OperationPriorities.Subtraction);
}
else if (token is MultiplyLexicToken)
{
return(OperationPriorities.Multiplication);
}
else if (token is DivideLexicToken)
{
return(OperationPriorities.Division);
}
else if (token is ModulusLexicToken)
{
return(OperationPriorities.Modulus);
}
else if (token is PowerLexicToken)
{
return(OperationPriorities.Power);
}
else if (token is FunctionLexicToken)
{
return(OperationPriorities.Function);
}
else if (token is FactorialLexicToken)
{
return(OperationPriorities.Function);
}
else
{
throw new NotSupportedException();
}
}
public LexerResult Evaluate(ILexerContext input)
{
InputStream stream = input.Stream;
List <LexicToken> tokens = new List <LexicToken>();
while (!stream.IsEmpty)
{
InputStream copy = stream;
foreach (TokenReader reader in input.Readers)
{
LexicToken token = null;
stream = reader.TryRead(stream, out token);
if (token != null && !(token is WhitespaceLexicToken))
{
if (token is NamedLexicToken)
{
NamedLexicToken nlt = (NamedLexicToken)token;
if (input.IsFunction(nlt.Name))
{
token = new FunctionLexicToken(nlt.Name);
}
else
{
token = new VariableLexicToken(nlt.Name);
}
}
tokens.Add(token);
break;
}
}
if (stream == copy)
{
throw new ParserException($"Unexpected character '{stream.Content[0]}' at position {stream.Position}");
}
}
this.ValidateLexingOutput(tokens);
return(new LexerResult(tokens));
}
