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class Lexer {
enum TokenType {
INTEGER = 0,
END_OF_FILE = 1,
IDENTIFIER = 2,
CHARACTER = 3
} _tokenType;
public:
Lexer(istream& in):
_in(in) {
nextToken();
}
bool match(char c) {
if ((_tokenType == IDENTIFIER &&
_identifier.size() == 1 &&
_identifier[0] == c) ||
(_tokenType == CHARACTER &&
_character == c)) {
nextToken();
return true;
} else
return false;
}
bool match(const char* str) {
if (_tokenType == IDENTIFIER &&
_identifier == str) {
nextToken();
return true;
} else
return false;
}
void expect(char expected) {
if (!match(expected)) {
cerr << "ERROR: expected '" << expected << "' but got ";
printToken(cerr);
cerr << '.' << endl;
exit(0);
}
}
void expectIdentifier(const char* str) {
if (!match(str)) {
cerr << "ERROR: expected \"" << str << "\" but got ";
printToken(cerr);
cerr << '.' << endl;
exit(0);
}
}
void expectEOF() {
ensureType(END_OF_FILE);
}
void readInteger(mpz_class& integer) {
ensureType(INTEGER);
integer = _integer;
nextToken();
}
void readInteger(unsigned int& i) {
ensureType(INTEGER);
if (!_integer.fits_uint_p()) {
cerr << "ERROR: expected 32 bit unsigned integer but got " << _integer << "." << endl;
exit(0);
}
i = _integer.get_ui();
nextToken();
}
void readIdentifier(string& identifier) {
ensureType(IDENTIFIER);
identifier = _identifier;
nextToken();
}
private:
int getChar() {
return _in.get();
}
int peek() {
return _in.peek();
}
void ensureType(TokenType type) {
if (_tokenType != type) {
cerr << "Expected ";
printTokenType(cerr, type);
cerr << " but got ";
printToken(cerr);
cerr << '.' << endl;
exit(0);
}
}
void eatWhite() {
while (isspace(peek()))
getChar();
}
void nextToken() {
eatWhite();
int c = peek();
if (c == EOF)
_tokenType = END_OF_FILE;
else if (isdigit(c)) {
_tokenType = INTEGER;
_in >> _integer;
} else if (c == '-' || c == '+') {
getChar();
eatWhite();
if (isdigit(peek())) {
_tokenType = INTEGER;
_in >> _integer;
if (c == '-')
_integer *= -1; // TODO: look up more efficient way to swap sign
} else {
_tokenType = CHARACTER;
_character = c;
}
} else if (isalpha(c)) {
_tokenType = IDENTIFIER;
_identifier.clear();
do
_identifier += getChar();
while (isalnum(peek()));
} else {
_tokenType = CHARACTER;
_character = getChar();
}
}
void printTokenType(ostream& out, TokenType type) {
switch (type) {
case END_OF_FILE:
out << "end of file";
break;
case INTEGER:
out << "an integer";
break;
case CHARACTER:
out << "a character";
break;
case IDENTIFIER:
out << "an identifier";
break;
default:
ASSERT(false);
}
}
void printToken(ostream& out) {
switch (_tokenType) {
case END_OF_FILE:
out << "end of file";
break;
case INTEGER:
out << _integer;
break;
case CHARACTER:
out << '\'' << _character << '\'';
break;
case IDENTIFIER:
out << '"' << _identifier << '"';
break;
default:
ASSERT(false);
}
}
mpz_class _integer;
string _identifier;
char _character;
istream& _in;
};
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