public Token scan() {
// skip empty symbols and comments
for (; ; readch()) {
if (peek == ' ' || peek == '\t') continue;
else if (peek == '\n') line++;
// skip comments
else if (peek == '/') {
readch();
if (peek == '/') {
do {
readch();
} while (peek != '\n');
line++;
} else if (peek == '*') {
for (; ; ) {
readch();
if (peek == '*') if (readch('/')) break;
if (peek == '\n') line++;
}
} else return new Token('/');
} else break;
}
// scan for not alone math symbols
switch (peek) {
case '&':
if (readch('&')) return Word.and;
else return new Token('&');
case '|':
if (readch('|')) return Word.or;
else return new Token('|');
case '=':
if (readch('=')) return Word.eq;
else return new Token('=');
case '!':
if (readch('=')) return Word.ne;
else return new Token('!');
case '<':
if (readch('=')) return Word.le;
else return new Token('<');
case '>':
if (readch('=')) return Word.ge;
else return new Token('>');
case '+':
if (readch('+')) return Word.inc;
else return new Token('+');
case '-':
if (readch('-')) return Word.dec;
else return new Token('-');
}
// found quotes, so parse sting for print
if (peek == '"') {
StringBuffer b = new StringBuffer();
readch();
while (peek != '"') {
// found slash, parse special symbol
if (peek == '\\') {
readch();
if (peek == 'n') b.append('\n');
else if (peek == 't') b.append('\t');
else if (peek == '\\') b.append('\\');
else if (peek == '\'') b.append('\'');
else if (peek == '\"') b.append('\"');
else throw new Error("Can't recognise symbol at " + line + " line");
} else b.append(peek);
readch();
}
readch();
return new Text(b.toString());
}
// scan for number
if (Character.isDigit(peek)) {
StringBuilder b = new StringBuilder();
do {
b.append(peek);
readch();
} while (Character.isDigit(peek));
// look is number were written in hex or bin format
if (peek == 'h' || peek == 'H') {
readch();
return new Number(Integer.parseInt(b.toString(), 16));
}
if (peek == 'b' || peek == 'B') {
readch();
return new Number(Integer.parseInt(b.toString(), 2));
}
// look is number float
if (peek != '.') return new Number(Integer.parseInt(b.toString()));
float x = Integer.parseInt(b.toString());
float d = 10;
for (; ; ) {
readch();
if (!Character.isDigit(peek)) break;
x = x + Character.digit(peek, 10) / d;
d = d * 10;
}
return new Real(x);
}
// scan for words
if (Character.isLetter(peek) || peek == '_') {
StringBuilder builder = new StringBuilder();
do {
builder.append(peek);
readch();
} while (Character.isLetterOrDigit(peek) || peek == '_');
String name = builder.toString();
Word word = words.get(name);
if (word != null) return word;
word = new Word(name, Tag.ID);
reserve(word);
return word;
}
// something other
Token t = new Token(peek);
peek = ' ';
return t;
}
public Lexer(InputStream src) {
this.source = src;
words = new Hashtable<>();
// reserve key words
reserve(new Word("for", Tag.FOR));
reserve(new Word("if", Tag.IF));
reserve(new Word("else", Tag.ELSE));
reserve(new Word("while", Tag.WHILE));
reserve(new Word("do", Tag.DO));
reserve(new Word("print", Tag.PRINT));
reserve(new Word("read", Tag.READ));
reserve(Word.True);
reserve(Word.False);
reserve(Type.Int);
reserve(Type.Bool);
reserve(Type.Float);
}