/// <summary>
/// Tokenizes <paramref name="expr"/>.
/// </summary>
/// <param name="expr">The expression.</param>
/// <returns>Tokens found <paramref name="expr"/>.</returns>
private List <string> Lexer(string expr)
{
var token = "";
var tokens = new List <string>();
expr = expr.Replace("+-", "-");
expr = expr.Replace("-+", "-");
expr = expr.Replace("--", "+");
for (var i = 0; i < expr.Length; i++)
{
var ch = expr[i];
if (char.IsWhiteSpace(ch))
{
continue;
}
if (char.IsLetter(ch))
{
if (i != 0 && (char.IsDigit(expr[i - 1]) || expr[i - 1] == ')'))
{
tokens.Add("*");
}
token += ch;
while (i + 1 < expr.Length && char.IsLetterOrDigit(expr[i + 1]))
{
token += expr[++i];
}
tokens.Add(token);
token = "";
}
else if (char.IsDigit(ch))
{
token += ch;
while (i + 1 < expr.Length && (char.IsDigit(expr[i + 1]) || (expr[i + 1] >= 'a' && expr[i + 1] <= 'f') || (expr[i + 1] >= 'A' && expr[i + 1] <= 'F') || expr[i + 1] == '.'))
{
token += expr[++i];
}
tokens.Add(token);
token = "";
}
else if (i + 1 < expr.Length && (ch == '-' || ch == '+') && char.IsDigit(expr[i + 1]) &&
(i == 0 || OperatorList.IndexOf(expr[i - 1].ToString(CultureInfo.InvariantCulture)) != -1 ||
(i - 1 > 0 && expr[i - 1] == '(')))
{
// if the above is true, then the token for that negative number will be "-1", not "-","1".
// to sum up, the above will be true if the minus sign is in front of the number, but
// at the beginning, for example, -1+2, or, when it is inside the brakets (-1).
// NOTE: this works for + as well!
token += ch;
while (i + 1 < expr.Length && (char.IsDigit(expr[i + 1]) || expr[i + 1] == '.'))
{
token += expr[++i];
}
tokens.Add(token);
token = "";
}
else if (ch == '(')
{
if (i != 0 && (char.IsDigit(expr[i - 1]) || char.IsDigit(expr[i - 1]) || expr[i - 1] == ')'))
{
if (tokens.Count > 0 && LocalFunctions.ContainsKey(tokens[tokens.Count - 1]) == true)
{
tokens.Add("(");
}
else
{
tokens.Add("*");
tokens.Add("(");
}
}
else
{
tokens.Add("(");
}
}
else
{
tokens.Add(ch.ToString());
}
}
return(tokens);
}
