IRC Hacks [Electronic resources] نسخه متنی

Hack 61 Perform Feats of Math

Lose your calculator. Evaluate mathematical
expressions with a bot that uses the Java Expression
Parser.

How many times have you been desperate
to find out the answer to a simple sum, only to discover that you
can't remember where you left your calculator? One
solution could be to fire up a calculator application on your
computer, but for IRC users, a solution can be found even closer to
home.

9.5.1 Java Expression Parser

The Java Expression Parser (JEP) is an
excellent tool for parsing and evaluating mathematical
expressions. This is ideal for use by bots, because it can take a
string as input, parse it, and evaluate the answer. This hack is
based on the 2.24 release, which is available for free at http://www.singularsys.com/jep.

JEP input can contain the usual +,
-, *, and /
symbols, along with ^ to raise powers. JEP
contains a set of standard constants, such as pi,
e, and i, and a standard set of
functions, such as sqrt, sin,
abs, and so on. JEP supports implicit
multiplication, where 2pi is automatically
interpreted as meaning 2 * pi.
Expressions like sqrt(-1) will not break JEP, as
it can handle complex arithmetic and give answers with both a real
and imaginary part.

9.5.2 The Code

This bot will make use of the JEP
and PircBot packages. It will respond to any channel messages of the
form calc expression.
If it is able to parse the expression correctly, it will give the
answer; otherwise, it will say it is unable to do so.

Save the following code as MathBot.java:

import org.jibble.pircbot.*;
import org.nfunk.jep.*;
public class MathBot extends PircBot {
// This JEP object will be used for the calculations.
private JEP jep;
public MathBot(String name) {
setName(name);
// Set up the JEP object's capabilities.
jep = new JEP( );
jep.addStandardConstants( );
jep.addStandardFunctions( );
jep.setAllowUndeclared(false);
jep.setImplicitMul(true);
jep.addComplex( );
}
public void onMessage(String channel, String sender,
String login, String hostname, String message) {
message = message.trim( ).toLowerCase( );
// Check for the "calc" command.
if (message.startsWith("calc ")) {
String expression = message.substring(5);
// Default answer.
String answer = "Unable to parse your input.";
try {
jep.parseExpression(expression);
if (!jep.hasError( )) {
String real = String.valueOf(jep.getValue( ));
String complex = String.valueOf(jep.getComplexValue( ));
answer = real;
// Remove the decimal point if the number is integral.
if (real.endsWith(".0")) {
answer = real.substring(0, real.length( ) - 2);
}
if (!complex.endsWith(" 0.0)")) {
answer = "Complex " + complex;
}
}
}
catch (Exception e) {
// Do nothing.
}
sendMessage(channel, sender + ": " + answer);
}
}
}

A main method is required to create
the bot and tell it to join a channel; we'll call it
MathBotMain.java:

public class MathBotMain {
public static void main(String[] args) throws Exception {
MathBot bot = new MathBot("MathBot");
bot.setVerbose(true);
bot.connect("irc.freenode.net");
bot.joinChannel("#irchacks");
}
}

9.5.3 Running the Hack

Compile the bot:

C:\java\MathBot> javac -classpath jep-2.24.jar;pircbot.jar;. *.java

Run it like so:

C:\java\MathBot> java -classpath jep-2.24.jar;pircbot.jar;. MathBotMain

You can see the bot in action in Figure 9-4.