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options{
//DEBUG_PARSER = true; DEBUG_TOKEN_MANAGER = true;
}
PARSER_BEGIN(Calculator)
import java.util.HashMap;
public class Calculator {
private static HashMap variables = new HashMap();
public static void main(String[] args) {
Calculator parser = new Calculator(System.in);
while (true){
System.out.print("Type your expression: ");
try{
Double value = parser.evaluateNextLine();
System.out.println("Returned: " + value);
}catch (ParseException e){ // Now we will parse the exception message to render it in our format.
if(e.getMessage().split("\n").length > 1){ // The error message is on multiple line -> it had been generated
int index = "Encountered: \"".length();
String em = e.getMessage().substring(index);
String token = em.substring(1,4);
if (token.equals("ILL")){ // Illegal token
em = em.substring(7);
index = em.indexOf("\"")-1;
if (index == 0){ // Special case in which the illegal token would be '"'
index = 2;
}
System.out.println("Illegal token: '"+ em.substring(0 , index) +"'.");
}else{ //Other generated error messages
index = em.indexOf("\"");
if (index == 0){ // Meaning the last token is not <TOK> but "char"
em = em.substring(1);
index = em.indexOf("\"");
}else{
index--;
}
System.out.println("Last read token: '"+ em.substring(0 , index)+"', w"+em.substring(em.indexOf("\nW")+2));
}
}else{ //Those were error messages created by ourselves, they are one line messages that we can directly print
System.out.println(e.getMessage());
}
try{
parser.passStatement(); // wiping the tokens of the malformed expression
}catch (ParseException ex){
System.out.println(ex.getMessage()); //not suppose to be possible to end up here
}
}
}
}
}
PARSER_END(Calculator)
SKIP : {
" "|"\t"
}
TOKEN : {
<EOL: "\n"|"\r">|
<PAL: "(">|
<PAR: ")">|
<ADD: "+">|
<SUB: "-">|
<MUL: "*">|
<DIV: "/">|
<EQU: "=">|
<LET: "let">|
<END: "exit">|
<NUM: (["0"-"9"])+("."((["0"-"9"])+))?>|
<ID: (["a"-"z"]|["A"-"Z"])+>|
<ILL: ~[]> // Defined so that I can 'wipe' the half parsed line in case of malformations
}
double statement() :
{
Token id;
double i = 0.0;
}
{
<END> { System.exit(0); }|
i=expression() { return i; }|
<LET> id=<ID> <EQU> i=expression()
{
variables.put(id.image,i); //Storing the variable
return i;
}
}
double expression() :
{
Token op = null;
double l = 0.0;
double r = 0.0;
}
{
l=term() ((op=<ADD> | op=<SUB>) r=term()
{ // folding everything in the l variable
if (op != null){
if (op.image.equals("+"))
l += r;
else
l -= r;
}
}
)*
{ //returning the parsed value
return l;
}
}
double term() :
{
Token op = null;
double l = 0.0;
double r = 0.0;
}
{
l=factor() ((op=<DIV> | op=<MUL>) r=factor()
{ // folding everything in the l variable
if (op != null){
if (op.image.equals("/"))
l /= r;
else
l *= r;
}
}
)*
{ //returning the parsed value
return l;
}
}
double factor() :
{
Token t = null;
Token id = null;
double i = 0.0;
}
{
(t=<NUM> | id=<ID> | <PAL> (i=expression()) <PAR>)
{
if(id != null){
Object var = variables.get(id.image);
if (var != null)
i = (double) var;
else
throw new ParseException("'" + id.image + "' is not yet defined.");
}else if(t != null)
i = Double.parseDouble(t.image);
return i;
}|
<SUB> (t=<NUM> | id=<ID> | <PAL> (i=expression()) <PAR>)
{
if(id != null){
i = (double)variables.get(id.image);
}else if(t != null)
i = Double.parseDouble(t.image);
return i*(-1);
}
}
double evaluateNextLine() :
{
double result = 0.0;
}
{
(result=statement()) <EOL> {
return result;
}|
<EOF>{System.out.println("\nBuffer was closed. Exiting."); System.exit(0);}
}
void passStatement() :
{
}
{
(<ILL>|<PAL>|<PAR>|<ADD>|<SUB>|<MUL>|<DIV>|<EQU>|<LET>|<END>|<NUM>|<ID>)* <EOL>| //Skip *anything* until the next EOL
<EOF>{System.out.println("\nBuffer was closed. Exiting."); System.exit(0);}|
{}
}
|
