Have you ever heard of F-Script? If you are a Cocoa developer I honestly hope you do. For those of you who haven’t, F-Script is supposed to be “A set of open source tools that complement Xcode and Interface Builder” that provide “Interactive introspection, manipulation and scripting of Cocoa objects”. So its a bunch of tools that allow you to interact with Objective-C and Cocoa during runtime through its own scripting mechanism, whose syntax differs significantly from the Objective-C language. So the line of source code…

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MyClass * var = [[MyClass alloc] initWithName:@"John"];

is written like the following in F-Script:

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var := MyClass alloc initWithName:'John'

If you download F-Script from www.fscript.org you end up with a bundle full of source code, executables and useful information. The most important are F-Script.app, FScript.framework and Extras/F-Script Anywhere.

Exploring Cocoa

The first file I mentioned — F-Script.app — is the toolchain in its simplest form: A script interpreter console. So what you can do is write your script lines to the console which will then be executed by the F-Script interpreter. For example: Writing the script line

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NSApplication sharedApplication terminate:nil

will make the application quit. But more interestingly, it gives you access to everything that is currently loaded into the Objective-C runtime. So you may create a window and populate it with UI through the F-Script console. Everything you can do from code in Xcode, you can do in F-Script through the console.

Debug Your Application

The second file — FScript.framework — is the most important one for developers. As you might guess, it is a framework that bundles all the F-Script functionality. If you’re writing a Cocoa application, add FScript.framework to your project and link against it. Somewhere in your loading code, insert the line

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[[NSApp mainMenu] addItem:[[[FScriptMenuItem alloc] init] autorelease]];

to add the F-Script menu to your main menu bar. What this gives you is a complete and immensly powerful scripting environment that is available to you at runtime. When you launch your app, go to the “F-Script” menu and choose “Show Console”. A new script interpreter will pop up ready to execute input from you through which you have access to all your objects: If your app has a controller object assigned as the app’s delegate, enter

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controller := NSApplication sharedApplication delegate

to assign the object to the controller script variable. So if your controller features the method -makeNoise, you can go ahead and hack

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controller makeNoise

into the script console and BOOM, your method gets called. What can you use this for? Obviously there’s no point in calling methods from the console that can also be executed through the press of a UI button. But if you’re developing a huge application that has some very complex functionality at its core, you’re very likely to end up with the situation that your core functionality is written and needs debugging, but lacking a user interface your app is not ready to take advantage of its core. Nevertheless you would like to debug the core you’ve written without having to go through the hassle of UI design yet. This is where F-Script comes in really handy. Launch the app, open the F-Script console and start debuggin your core! It’s all there right at your fingertips, ready to be thoroughly tested and evaluated, checked for bugs and all the other nasty app-killers.

That’s exactly what I did with Artifica today. Obviously writing a user interface for an application with the complexity of an image editor is no easy task and introduces a completely new source of bugs to your application. Therefore, I wrote the layer architecture from A to Z with the only testing UI available being a NSView that draws the final result of the layer rendering. As usually, after finishing the layering mechanism and launching the app for a try, everything stayed gray and empty. Bug. So I thought about the best way of debuggin the app. Writing some debugging code that created layers somewhere in the launch code of the app? Nah… that’s kind of lame and not very efficient. That was when I remembered F-Script. So I went to the website, grabbed my copy of it and added the framework and menu item to my app. And suddenly I was able to conduct the most thorough testing of my layers without having to create some testing UI for doing so. But not only does F-Script serve as a replacement for UI, it is also very useful for debugging. If you set one of your layer’s properties for example and nothing changes on the final result, you can use F-Script to inspect the layer object and look for where your updating mechanism broke down.

F-Script adds an invaluable means of debugging to your application. Things that were very uncomfortable to do beforehand, now are easy and fast. And if you have some frequently used object, for example your controller object, all you have to do is simply call

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FSInterpreter * interpreter = [[fscriptMenuItem interpreterView] interpreter];
[interpreter setObject:[NSApp delegate] forIdentifier:@"controller"];

with fscriptMenuItem being the FScriptMenuItem you added to the main menu before. This line will assign your app’s delegate to the “controller” script variable which you may then use during debugging to directly access your controller object.

Code Injection

The third important part of the tools is the F-Script Anywhere application. What this application does is that it allows you to inject F-Script into running Cocoa applications. When you do that, the running application gets a “F-Script” menu item which gives you a means to inspect and experiment with that app through the console and object browser. This technique is very useful if you want to know how some of the private APIs work or just want to know how another application is structured.

F-Script saves the Day

Being very robust and extremely powerful, F-Script is the ultimate tool for debuggin, inspecting or hacking other applications. As a developer, the most valuable thing you can do with F-Script is to include the framework into your application and use the console and object browser for debugging. It saves you hours of debugging hassle since you don’t have to return to your source code and recompile everytime you want to check whether some operation returned a valid value. But most of all, you don’t have to write any specific debuggin code to your app except the creation of the menu item and maybe the declaration of the most important objects in the F-Script namespace for easy access.

If it weren’t for F-Script, I would have spent 5 hours today writing debugging code and creating some testing UI for Artifica which would have been another source for bugs which increases complexity of the debugging process again. F-Script gives you the possibility to completely split up the development of your object model and your view model, which not only saves you a lot of time and is more productive, but is also less frustrating since you never have to go figure whether your app’s functionality is broken due to a bug in the UI, the object model or even worse, somewhere in between.

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Thanks for reading and enjoy coding with F-Script! It really is worth the 20 minutes of getting used to the scripting syntax!
Cheers