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The Waikato Environment for Knowledge Analysis (WEKA), a machine learning workbench. This version represents the developer version, the "bleeding edge" of development, you could say. New functionality gets added to this version.
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/*
 * STANDARD ML OF NEW JERSEY COPYRIGHT NOTICE, LICENSE AND DISCLAIMER.
 * 
 * Copyright (c) 1989-1998 by Lucent Technologies
 * 
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose and without fee is hereby granted, provided
 * that the above copyright notice appear in all copies and that both the
 * copyright notice and this permission notice and warranty disclaimer appear
 * in supporting documentation, and that the name of Lucent Technologies, Bell
 * Labs or any Lucent entity not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior permission.
 *
 * Lucent disclaims all warranties with regard to this software, including all
 * implied warranties of merchantability and fitness. In no event shall Lucent
 * be liable for any special, indirect or consequential damages or any damages
 * whatsoever resulting from loss of use, data or profits, whether in an action
 * of contract, negligence or other tortious action, arising out of or in
 * connection with the use or performance of this software. 
 *
 * Taken from this URL:
 * http://www.smlnj.org/license.html
 * 
 * This license is compatible with the GNU GPL (see section "Standard ML of New
 * Jersey Copyright License"):
 * http://www.gnu.org/licenses/license-list.html#StandardMLofNJ
 */

/*
 * Copyright 1996-1999 by Scott Hudson, Frank Flannery, C. Scott Ananian
 */

package weka.core.mathematicalexpression;

import java_cup.runtime.*;

import java.io.*;
import java.util.*;

/**
 * A parser for parsing mathematical expressions.
 *
 * @author FracPete (fracpete at waikato dot ac dot nz)
 * @version $Revision: 4939 $
 */

parser code {:
  /** variable - value relation. */
  protected HashMap m_Symbols = new HashMap();

  /** for storing the result of the expresion. */
  protected Double m_Result = null;

  /**
   * Sets the variable - value relation to use.
   * 
   * @param value the variable-value relation
   */
  public void setSymbols(HashMap value) {
    m_Symbols = value;
  }

  /**
   * Returns the current variable - value relation in use.
   * 
   * @return the variable-value relation
   */
  public HashMap getSymbols() {
    return m_Symbols;
  }

  /**
   * Sets the result of the evaluation.
   * 
   * @param value the result
   */
  public void setResult(Double value) {
    m_Result = value;
  }

  /**
   * Returns the result of the evaluation.
   * 
   * @return the result
   */
  public Double getResult() {
    return m_Result;
  }

  /**
   * Runs the parser from commandline. Either reads lines from System.in
   * or from a provided file (line by line). With 
   * -symbols 
   * as first parameter one can provide predefined variable values. E.g.:
   * -symbols "Y=10;X=3" "X+Y"
   * 
   * @param args the commandline arguments
   * @throws Exception if something goes wrong
   */
  public static void main(String args[]) throws Exception {
    // read symbols, if present
    HashMap symbols = new HashMap();
    if (args.length > 0) {
      if (args[0].equals("-symbols")) {
        // parse symbols
        String[] pairs = args[1].replaceAll(" ", "").split(";");
        for (int i = 0; i < pairs.length; i++) {
          String[] parts = pairs[i].split("=");
          symbols.put(parts[0], new Double(parts[1]));
        }
        // print symbols
        System.out.println("\nSymbols provided:");
        Iterator iter = symbols.keySet().iterator();
        while (iter.hasNext()) {
          String key = (String) iter.next();
          System.out.println(key + "=" + symbols.get(key));
        }
        // remove symbols from commandline
        String[] argsNew = new String[args.length - 2];
        System.arraycopy(args, 2, argsNew, 0, argsNew.length);
        args = argsNew;
      }
    }

    // setup input stream
    int index = -1;
    if (args.length == 1)
      index = 0;
    BufferedReader input = null;
    if (index == -1) {
      System.out.println("\nPlease type in expressions (and press ), exit with :");
      input = new BufferedReader(new InputStreamReader(System.in));
    }
    else {
      System.out.println("\nReading expressions from file '" + args[index] + "':");
      input = new BufferedReader(new FileReader(args[index]));
    }

    // process stream
    SymbolFactory sf = new DefaultSymbolFactory();
    String line;
    while ((line = input.readLine()) != null) {
      ByteArrayInputStream parserInput = new ByteArrayInputStream(line.getBytes());
      Parser parser = new Parser(new Scanner(parserInput,sf), sf);
      parser.setSymbols(symbols);
      parser.parse();
      System.out.println(line + " = " + parser.getResult());
    }
  }
:}

terminal COMMA, LPAREN, RPAREN;
terminal MINUS, PLUS, TIMES, DIVISION;
terminal ABS, SQRT, LOG, EXP, SIN, COS, TAN, RINT, FLOOR, POW, CEIL, IFELSE;
terminal TRUE, FALSE, LT, LE, GT, GE, EQ, NOT, AND, OR;
terminal Double NUMBER;
terminal Boolean BOOLEAN;
terminal String VARIABLE;

non terminal expr_list, expr_part;
non terminal Double expr;
non terminal Double opexpr;
non terminal Double varexpr;
non terminal Double funcexpr;
non terminal Boolean boolexpr;

precedence left PLUS, MINUS;
precedence left TIMES, DIVISION;
precedence left LPAREN, RPAREN;
precedence left ABS, SQRT, LOG, EXP, SIN, COS, TAN, RINT, FLOOR, POW, CEIL;
precedence left AND, OR;
precedence left NOT;

expr_list ::= expr_list expr_part | expr_part;
expr_part ::= expr:e {: parser.setResult(e); :} ;
expr      ::=   NUMBER:n
                {: RESULT = n; :}
              | LPAREN expr:e RPAREN
                {: RESULT = e; :}
              | opexpr:o
                {: RESULT = o; :}
              | varexpr:v
                {: RESULT = v; :}
              | funcexpr:f
                {: RESULT = f; :}
              ;

opexpr    ::=   expr:l PLUS expr:r
                {: RESULT = new Double(l.doubleValue() + r.doubleValue()); :}
              | expr:l MINUS expr:r
                {: RESULT = new Double(l.doubleValue() - r.doubleValue()); :}
              | expr:l TIMES expr:r
                {: RESULT = new Double(l.doubleValue() * r.doubleValue()); :}
              | expr:l DIVISION expr:r
                {: RESULT = new Double(l.doubleValue() / r.doubleValue()); :}
              ;

varexpr  ::=    VARIABLE:v
                {: if (parser.getSymbols().containsKey(v)) 
                     RESULT = (Double) parser.getSymbols().get(v); 
                   else 
                     throw new IllegalStateException("Unknown symbol '" + v + "'!"); 
                :}
              ;

funcexpr ::=    ABS LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.abs(e)); :}
              | SQRT LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.sqrt(e)); :}
              | LOG LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.log(e)); :}
              | EXP LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.exp(e)); :}
              | SIN LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.sin(e)); :}
              | COS LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.cos(e)); :}
              | TAN LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.tan(e)); :}
              | RINT LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.rint(e)); :}
              | FLOOR LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.floor(e)); :}
              | POW LPAREN expr:base COMMA expr:exponent RPAREN
                {: RESULT = new Double(Math.pow(base, exponent)); :}
              | CEIL LPAREN expr:e RPAREN
                {: RESULT = new Double(Math.ceil(e)); :}
              | IFELSE LPAREN boolexpr:b COMMA expr:e_true COMMA expr:e_false RPAREN
                {: if (b) 
                     RESULT = e_true; 
                   else
                     RESULT = e_false; 
                :}
              ;

boolexpr ::=    BOOLEAN:b 
                {: RESULT = b; :}
              | TRUE
                {: RESULT = new Boolean(true); :}
              | FALSE
                {: RESULT = new Boolean(false); :}
              | expr:l LT expr:r
                {: RESULT = new Boolean(l.doubleValue() < r.doubleValue()); :}
              | expr:l LE expr:r
                {: RESULT = new Boolean(l.doubleValue() <= r.doubleValue()); :}
              | expr:l GT expr:r
                {: RESULT = new Boolean(l.doubleValue() > r.doubleValue()); :}
              | expr:l GE expr:r
                {: RESULT = new Boolean(l.doubleValue() >= r.doubleValue()); :}
              | expr:l EQ expr:r
                {: RESULT = new Boolean(l.doubleValue() == r.doubleValue()); :}
              | LPAREN boolexpr:b RPAREN
                {: RESULT = b; :}
              | NOT boolexpr:b
                {: RESULT = !b; :}
              | boolexpr:l AND boolexpr:r
                {: RESULT = l && r; :}
              | boolexpr:l OR boolexpr:r
                {: RESULT = l || r; :}
              ;