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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){
System.out.println(e.getMessage());
try{
parser.passStatement(); // wiping the tokens of the malformed expression
}catch (ParseException ex){
System.out.println(ex.getMessage());
}
}
}
}
}
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"])+>
}
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() :
{}
{
<EOL>|
<EOF>{System.out.println("\nBuffer was closed. Exiting."); System.exit(0);}
}
|
