public Element[] Parse(string exprString, int endIndex, out int lastMatchedIndex)
{
parser_error = "";
//为了防止在词法分析过程中出现字符串数组越界，在末尾补上无效字符
exprString = exprString.Insert(endIndex, "~~~~~~");
Element[] Sequence = new Element[maxLength];
int seqIndex = 0;
Element var = new Element(Token.Variable);
lastMatchedIndex = -1;
for (int i = 0; i < exprString.Length; i++)
{
if (exprString[i] == ' ')
{
}
//符号是数字
else if (char.IsNumber(exprString[i]))
{
int j = i;
double value = 0;
while (j < exprString.Length && ((exprString[j] <= '9' && exprString[j] >= '0') || exprString[j] == '.'))
{
j++;
}
try
{
value = Double.Parse(exprString.Substring(i, j - i));
}
catch (FormatException fe)
{
parser_error += "数字格式错误！\n";
Sequence[seqIndex++] = new Element(Token.Null);
return(Sequence);
}
Sequence[seqIndex++] = new Element(Token.Number, value);
i = j - 1;
}
//符号是保留字
else if (char.IsLower(exprString[i]))
{
List <string> Candiates = Symbols.LongestMatch(exprString, i, endIndex, out int lastMatchedIndex_1);
if (Candiates.Count == 1 && Candiates[0].Length == lastMatchedIndex_1 - lastMatchedIndex)
{
Sequence[seqIndex++] = new Element(Symbols.SymbolToToken[Candiates[0]]);
if (Sequence[seqIndex - 1].token == Token.Variable)
{
Sequence[seqIndex - 1] = var;
}
i = lastMatchedIndex_1;
}
else
{
parser_error += "未找到该标识符！\n";
Sequence[seqIndex++] = new Element(Token.Null);
return(Sequence);
}
}
//符号是单个字符的情况
else
{
switch (exprString[i])
{
case '+': Sequence[seqIndex++] = new Element(Token.Add); break;
case '-': Sequence[seqIndex++] = new Element(Token.Sub); break;
case '*': Sequence[seqIndex++] = new Element(Token.Mul); break;
case '/': Sequence[seqIndex++] = new Element(Token.Div); break;
case '^': Sequence[seqIndex++] = new Element(Token.Pow); break;
case '(': Sequence[seqIndex++] = new Element(Token.Lparen); break;
case ')': Sequence[seqIndex++] = new Element(Token.Rparen); break;
case ',': Sequence[seqIndex++] = new Element(Token.Comma); break;
case '~': Sequence[seqIndex++] = new Element(Token.Null); break;
default: Sequence[seqIndex++] = new Element(Token.Null);
parser_error += "错误符号！\n"; return(Sequence);
}
}
lastMatchedIndex = i;
}
Sequence[seqIndex++] = new Element(Token.Null);
return(Sequence);
}