Someone

import java.util.HashMap;import java.util.Map;import java.util.Stack;import java.util.StringTokenizer;import java.util.regex.Pattern;public class BasicInterpreter {	private static enum Operation {		ADD("+"){double operate(double x, double y) { return x+y; }},		SUBTRACT("-"){double operate(double x, double y) { return x-y; }}, 		DIVIDE("/"){double operate(double x, double y) { return x/y; }},		MULTPLY("*"){double operate(double x, double y) { return x*y; }};		String name;		private Operation(String name) {			this.name = name;		}		abstract double operate (double x, double y);		public static Operation parseString(String str) {			for(Operation o : Operation.values()) {				if(str.equals(o.name)) return o;			}			return null;		}	}	private Map<String,Double> symbolTable;	public BasicInterpreter() {		symbolTable = new HashMap<String,Double>();	}	public void parseLine(String line) {		String[] tokens = line.split(" ");		for(String s:tokens) System.out.println(s); //debug		if(tokens[0].equals("let")) {			// assignment code here			String name = tokens[1];			String expr = line.split("=")[1];			symbolTable.put(name, evaluate(expr.substring(1,expr.length())));			System.out.println("OK");		} else if (tokens[0].equals("print")) {			String expr = line.replaceFirst("print ", "");			System.out.println(evaluate(expr));			// print code here		} else {			System.err.println("Error: Unknown command '" + tokens[0] + "'");		}	}		private double evaluate(String expr) {		System.out.println("expr = " + expr);		String[] tokens = expr.split(" ");		Pattern ops = Pattern.compile("[\\+\\-\\*\\/\\^]");		String expression = "";		for(int i = 0 ; i < tokens.length ; i++) {			System.out.println("tokens[" + i + "] is \"" + tokens[i] + "\"");//debug			if(!Character.isDigit(tokens[i].charAt(0)) && !ops.matcher(tokens[i]).matches()) {				tokens[i] = ""+symbolTable.get(tokens[i]);			}		}		String finalExpr = "";		for(String s:tokens) finalExpr += s + " ";		finalExpr = finalExpr.substring(0,finalExpr.length()-1); // strip trailing space		return new StackCalculator().evaluate(finalExpr);	}		/**	 * 	 * @author Brad Lindemann	 *	 */	private static class StackCalculator {		public double evaluate(String prob) {			int par1=0;			int par2=0;			for(int i = 0 ; i< prob.length() ; i++) {				if(prob.charAt(i) == '('){					par1 = i;					for (int j = prob.length() -1 ; j > par1 ; j--) {						if(prob.charAt(j) == ')') {							par2 = j;							break;						}					}					break;				}			}			if(par1 > par2)				throw new Error("Unclosed Parenthesis?");			if(par1 != par2)				prob = prob.substring(0,par1) + 					evaluate(prob.substring(par1+1,par2)) +					prob.substring(par2+1,prob.length());			split(prob.replaceAll(" ", ""));			return solveStack();		}				private void split(String stat) {			Stack<String> temp = new Stack<String>();			if(stat.length() < 2) {				temp.push(stat);			} else {				int pos = 0;				for(int i = 0 ; i < stat.length() ; i++) {					if(!Character.isDigit(stat.charAt(i))) {						temp.push(stat.substring(pos, i));						temp.push(""+stat.charAt(i));						pos = i+1;					}				}				temp.push(stat.substring(pos,stat.length()));			}			while(!temp.isEmpty()) {				if(Character.isDigit(temp.peek().charAt(0))) {					numbers.push(temp.pop());				} else {					operators.push(temp.pop());				}			}		}				private double solveStack() {			int level = 0;			Stack<String> tempNum = new Stack<String>(), tempOp = new Stack<String>();			while(level < priority.length) {				while(!operators.isEmpty()) {					if(tempOp.push(operators.pop()).equals(""+priority[level])) {						tempNum.push(numbers.pop());						switch(tempOp.pop().charAt(0)) {							case '^':								tempNum.push(""+Math.pow(Double.parseDouble(tempNum.pop()),										Double.parseDouble(numbers.pop())));								break;							case '*':								tempNum.push(""+Double.parseDouble(tempNum.pop()) *										Double.parseDouble(numbers.pop()));								break;							case '/':								tempNum.push(""+Double.parseDouble(tempNum.pop()) /										Double.parseDouble(numbers.pop()));								break;							case '-':								tempNum.push(""+(Double.parseDouble(tempNum.pop()) -										Double.parseDouble(numbers.pop())));								break;							case '+':								tempNum.push(""+(Double.parseDouble(tempNum.pop()) +										Double.parseDouble(numbers.pop())));								break;							default:								throw new Error("Invalid operator");						}						while(!tempNum.isEmpty()) {							numbers.push(tempNum.pop());						}						while(!tempOp.isEmpty()) {							operators.push(tempOp.pop());						}					}else {						tempNum.push(numbers.pop());					}				}				while(!tempNum.isEmpty()) numbers.push(tempNum.pop());				while(!tempOp.isEmpty()) operators.push(tempOp.pop());				level++;			}			return Double.parseDouble(numbers.pop());		}				private Stack<String> numbers = new Stack<String>();		private Stack<String> operators = new Stack<String>();		public static final char[] priority = {'^','*','/','+','-'};	}	}