public static Token Scan()
{
//去除空白
for (; !EofReached; ReadChar())
{
if (peek == ' ' || peek == '\t')
{
}
else if (peek == '\r')
{
ReadChar();
++line;
}
else
{
break;
}
}
if (EofReached)
{
return(null);
}
//检测注释
if (peek == '/')
{
ReadChar();
switch (peek)
{
case '/': for (; ; ReadChar())
{
if (peek == '\r' || peek == '\uffff')
{
return(Scan());
}
}
case '*':
for (ReadChar(); ; ReadChar())
{
switch (peek)
{
case '\r':
line++;
ReadChar();
break;
case '*':
ReadChar();
if (peek == '/')
{
ReadChar();
return(Scan());
}
break;
case '\uffff':
return(Scan());
}
}
}
return(new Token('/'));
}
//操作符
switch (peek)
{
case '&':
return(ReadChar('&') ? Word.And : new Token('&'));
case '|':
return(ReadChar('|') ? Word.Or : new Token('|'));
case '=':
return(ReadChar('=') ? Word.Equal : new Token('='));
case '!':
return(ReadChar('=') ? Word.NotEqual : new Token('!'));
case '<':
return(ReadChar('=') ? Word.Less : new Token('<'));
case '>':
return(ReadChar('=') ? Word.Greater : new Token('>'));
case '"':
var s = "";
ReadChar();
for (; ; ReadChar())
{
switch (peek)
{
case '"':
{
ReadChar();
return(new String(s));
}
case '\n':
{
//Error("应输入\"\"\"");
ReadChar();
return(new String(s));
}
}
s = s + peek;
}
}
//分析数字
if (char.IsDigit(peek))
{
var val = 0;
do
{
val = 10 * val + (peek - '0'); ReadChar();
} while (char.IsDigit(peek));
if (peek != '.')
{
return(new Int(val));
}
float float_val = val;
for (float d = 10; ; d *= 10)
{
ReadChar();
if (!char.IsDigit(peek))
{
break;
}
float_val += (peek - 48) / d;
}
return(new Float(float_val));
}
//分析标识符
if (char.IsLetter(peek))
{
var b = new StringBuilder();
do
{
b.Append(peek);
ReadChar();
} while (char.IsLetterOrDigit(peek));
var s = b.ToString();
if (key_words.ContainsKey(s))
{
return(key_words[s]);
}
return(key_words[s] = new Word(s, Tag.ID));
}
//其他符合
var tok = new Token(peek);
if (!EofReached)
{
peek = ' ';
}
return(tok);
}
private static void Reserve(Word word) => key_words.Add(word.lexeme, word);