I remember a particularly long weekend sitting in a computer lab for 12 hours and trying to write an assembler program on a VAX machine that would read and write files. (A VAX is a big archaic mainframe computer.)

It took many days, but I was finally able to provide successful results. Sometimes, I think we take for granted that ColdFusion makes our lives extremely easy. (Even a novice CF developer should be able to figure out how to read and write files in under five minutes.) One tool that was integral to my success in the project was the use of an interactive debugger. In my professional career, I've used one for writing Pascal and Lotus Notes, but, moving to the Web world, debuggers were noticeably vacant. That is until now. The folks who brought us Fusion Reactor have now brought us FusionDebug, the first interactive debugger for ColdFusion MX.

Why Do You Need an Interactive Debugger?
What is an interactive debugger? It is a tool that allows you to view the results of your code, line by line. You can see the value of variables, queries, CFC Instances, and change the values of variables on the fly. If you slip back into the old days of your memory, you probably remember a product called ColdFusion Studio, right? Before CFEclipse, ColdFusion Studio was the tool that (almost) everyone used for creating ColdFusion applications. A little known (and even lesser used) feature in CF Studio was the availability of an interactive debugger. Unfortunately, the product was hard to configure and even harder to use, so it never became a staple of the ColdFusion developer's toolbox. Today, the landscape of ColdFusion development is much different than it was in the CF Studio days. In the old days, most templates did multiple things and business logic code was implemented right next to display logic. There was little thought of code encapsulation, and templates were written the same way they were processed (start at the top and work your way down). Although CFML custom tags and User-Defined Functions provided facilities for encapsulating code, it wasn't until ColdFusion Components were introduced that people started to apply advanced programming principles to their ColdFusion applications. Business logic is now put inside of CFCs. Frameworks such as Model-Glue and Mach-II help us separate business logic and presentation code. When a single ColdFusion page loads, it may be performing actions where the code is located across multiple files. It isn't always easy to find the root of your errors. FusionDebug is a tool that will help you find and correct your troublesome code.

I thought a good place to start might be to offer a definition of debugging concepts and definitions:

• Breakpoint: A breakpoint is a spot in your code where you want the debugger to stop, and can be any line with CFML code (tags, variables, and so on). After starting a debug session in FusionDebug, you'll load the page you want to debug in the browser and FusionDebug will intercept it at your first breakpoint. (It can also intercept requests from pages and CFCs called from Flex, AJAX, Flash Remoting, and Web services.) If there are no breakpoints, the page will run as normal. Breakpoints do not have to be in the page you request, they can be located in CFCs, custom tags, includes, or UDFs.
• Variables: You already know what a variable is and how to use them. (If not, read "Creating Variables in CFML" from CFDJ, Vol. 6, issue 2 [http://coldfusion.sys-con.com/read/43790.htm]). The variable list of FusionDebug shows all of the variables currently available to the template you are in, at the point where you're debugging. It will display local variables (the variables scope), URL, Form, request, CGI, and cookie variables, as well as shared-scope variables like session and application, and more.
• Expressions: In the past I've always referred to these as "watch variables." Expressions, in its simplistic form, are variables that you want to keep tabs on. However, the expression pane of FusionDebug will support any ColdFusion expression. Perhaps you want to keep tabs on what the first item of a list is, or the last element in an array? You can do that with the Expression tab.
• Debug: The debug command means to starts a debugging session. In other software I've seen this described as "run" or "execute."
• Step Into: A step is how you move from one line of code to the next. There are three variations of the Step depending on what you want to do. Step Into is probably what you'll use most of the time. It means to step over this line of code, but jump into any functions, custom tags, or CFC method calls that are called from the line of code you're on. FusionDebug will open the file that you step into and stop at the first line of CFML code.
• Step Over: Step Over is the exact opposite of Step Into. It will execute the code in any function, custom tag, or CFC Method without opening it. It moves right onto the next line. It's a good idea to favor Step Over even on tags and expressions that wouldn't open a file, for reasons I'll explain later.
• Step Return: Step Return is used when you're inside a file that you stepped into. It will execute the rest of the file, and put you back to the place where the file was initially stepped into
• Resume: Resume means to continue execution of code until you run out of code, or find another breakpoint.
• Terminate: Terminate will end the debugging session without completing your code's execution. Usually I try to avoid using this.

Installing FusionDebug
FusionDebug is created as an eclipse plug in. and you'll need Eclipse to install it. If you're already using CFEclipse or FlexBuilder, you must already have Eclipse installed. If not, you can download Eclipse from www.eclipse.org/. It's as simple as extracting a zip file and running the Eclipse command. There's no installer.

Speaking of CFEclipse, which is another plug-in for editing CFML code, while you don't need to use it with FusionDebug, if you want to try it, I strongly recommend reading the ACME (Apache, ColdFusion, MySQL, Eclipse) guide for detailed instructions (www.stephencollins.org/acme/) on the install. Even if you don't use Apache or MySQL look at just the final chapter on CFEclipse. It's the best place to find detailed installation instructions on CFEclipse. There are two ways to install FusionDebug: using a manual process or an automated one. The automated process uses the "Find and Install Updates" feature built into Eclipse. This is documented in the FusionDebug user guide, which (at the time of this writing) is available at www.fusion-reactor.com/fusiondebug/helpDocs/FusionDebug_User_Guide.pdf. I'm going to step you through the process of the manual install, so while you're at it you may as well download the files for a manual install. The zip archive includes the PDF documentation at "plugins\com.intergral.fusionreactor.debug.core_1.0.0\FusionDebug - User manual.pdf". No matter which way you install, I recommend reading through the guide. Plugins for Eclipse are located in a subdirectory of your Eclipse installation named plugins. You can unzip the download to the plugins directory if you wish. Restart Eclipse so the plugin is found. If you don't wish to extract into your Eclipse directory, unzip somewhere else, and copy the directories manually. There are two directories you need to put in "eclipseinstall\plugins": "com.intergral.fusionreactor.debug.core_1.0.0" and "com.intergral.fusionreactor.debug.ui_1.0.0". Restart Eclipse and you should be good to go. Yes, the install really is as easy as copying files.