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import java.io.IOException;
import java.io.Reader;
import java.util.Hashtable;
import java.util.Map;
public class Lexer
{
private Reader in;
private int x;
private Map<String,Token.T> reserved =
new Hashtable<String,Token.T>();
public Lexer(Reader in) throws IOException
{
this.in = in;
x = in.read();
reserved.put("let", Token.T.LET);
// acrescentar demais palavras reservadas
// ...
}
public Token get() throws IOException
{
// retornar o próximo símbolo léxico do programa
while (Character.isWhitespace(x))
x = in.read();
if (x == -1)
return new Token(Token.T.EOF);
if ((char)x == ',')
{
x = in.read();
return new Token(Token.T.COMMA);
}
if (Character.isDigit(x))
{
StringBuilder builder = new StringBuilder();
builder.append((char)x);
while (Character.isDigit((x = in.read())))
builder.append((char)x);
return new Token(Token.T.INT, new Long(builder.toString()));
}
if (Character.isAlphabetic(x))
{
StringBuilder builder = new StringBuilder();
builder.append((char)x);
while (Character.isAlphabetic(x = in.read()) ||
Character.isDigit(x) || (char)x == '_')
builder.append((char)x);
String s = builder.toString();
Token.T t = reserved.get(s);
if (t == null)
return new Token(Token.T.ID, s);
return new Token(t);
}
// completar demais tokens
System.out.println("unexpectec char: <" + (char)x + ">");
x = in.read();
return get();
}
}
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