Passing code as a text stream into a program

A text stream is a line of text terminated by the newline character, '\n'. The standard library function getchar() retrieves one character at a time from the text stream. 


In the first chapter of Kernighan and Ritchie's The C Programming Language 2e, this function is used in programs of increasing complexity, from a character counter to a rudimentary syntax checker. 


Testing these programs in Xcode's Debugger Console can only be very limited. As soon as the user presses Enter, the text stream is happily processed, and the program expects additional input. But what if you want to test input spanning multiple lines?

In K&R C section 1.6, the first example program counts the frequency of different characters, like digits and blanks. Sample output is from "the program on itself." Near the end of the chapter, Exercise 1-23 asks to "write a program to remove all comments from a C program." There has to be some way to pre-populate the text stream, so that your program processes it to an EOF. 


Using cat, we can pipe the output of a file, such as main.c, to our program. Since we're using Xcode, the path to our project directory can be pretty long to type every time. Instead, we'll write an AppleScript script to tell Xcode to build the project, and to tell Terminal to activate and execute the cat pipe:

The script uses some parts from my previous AppleScript tutorial. Fortunately, all paths are POSIX formatted rather than aliases formatted as HFS paths.  


The one new thing is the use of quoted form, which lets me pass a directory with spaces, like /Programming Exercises/, without escaping the blanks.


With this script, the same program now processes a text stream all the way to EOF:

And the output:

I'm not sure how much use this will be beyond the first chapter, but now that I can pass text streams to EOF in my programs, I feel better about going through these exercises. Instead of one-liner "tests," I can pass whole files as representative input.


References

• Quoted form property of the text object, AppleScript Language Guide

Setting up Flex, flixel and Xcode

In this tutorial, you will build and run a flixel project from Xcode. You will use Xcode to edit ActionScript 4 files, and you will see how Xcode uses an External Build Target to run the AS4 compiler mxmlc, much like how Eclipse uses javac behind the scenes to compile .java files, or how Mac OS X uses open to launch Preview when you double-click on a PDF file. At the end of this post, you will find links to three comprehensive, excellent flixel tutorials.

Flixel is a game development library created by Adam Saltsman that leverages the Adobe Flex framework. Both the flixel library and the Flex SDK will be needed. Additional files include the flixel template file and the syntax highlighter specification folder (SHSF). The template file will make things easier for both of us: first, your project should build out of the box: you'll have a working flixel application right from the start, in Xcode. Second, many steps can be referenced rather than explicitly enumerated. 

The SHSF has files to enable syntax highlighting of AS4 files in Xcode. We will use the specification files of Nathan Roberton, a UX designer in CTO Product Incubation at Microsoft. 

Before we begin, please note that this tutorial is for flixel 2.35, Adobe Flex 4.1.0.16076 and Xcode 3.2.2. I assume you have Xcode installed. Let's get started.

The tutorial has the following steps:

1. Download files.
2. Move and rename files.
3. Open Xcode, start a new flixel project, and build.
4. Run the SWF in Safari.

Step 1: Download files.

We need to download the following: 

• flixel 2.35
• Adobe Flex 4 SDK
• flixel template for Xcode
• syntax highlighter specification folder*

* The last download goes to Nathan Roberton's own tutorial on Xcode and AS3. Scroll to the bottom, to step eight, and download the "Actionscript specification files." 

Extract any compressed files.

Step 2: Move and rename files.

Next, move the flixel folder and the Flex SDK folder to the /Developer/Library/SDKs directory. 

Move the "Flixel Game" folder to the ~/Library/Application Support/Developer/Shared/Xcode/Project Templates/Other directory. 

Move the individual specification files into the ~/Library/Application Support/Developer/Shared/Xcode/Specifications directory. 

You will need to make folders, because some of these directories will not exist. 

At this point, you are free to rename the flixel library folder and the Flex SDK folder. For the purposes of this tutorial, rename them to "flixel_2.35" and "flex_4.1.0.16076," respectively. Omit the double quotes.

Why these specific directories? The Flex SDK is 273 MB, and I do not want Time Machine to back it up if I place it in my ~ (home) directory. The /Developer/SDKs directory is for "system SDKs," according to the Xcode Installation Guide. 

Step 3: Open Xcode, start a new flixel project, and build.

Launch Xcode. Go to File -> New Project. Choose "Other" under User Templates, select the "Flixel Game" template, and click Choose. Name your new project.

Under the Groups & Files sidebar, expand Targets, and then double-click on "mxmlc." Note the following:

• In the Build Tool field, the path leads to the mxmlc program. This is the Adobe Flex compiler. 
• In the Arguments field, there are two flags set: -compiler.source-path, and -static-link-runtime-shared-libraries=true. The first flag refers the compiler to the flixel libraries, and the second fixes an obscure [Embed()] issue. 
• In the Product Name field, note that spaces must be escaped, and that decimals are okay. Also notice the shorthand ${PRODUCT_NAME} used in the Arguments field.
• In the Build Settings section lower down, there is only PRODUCT_NAME. Most default Xcode projects will have GCC environment variables set here. They have been removed, because we are making SWFs. (Oh, and "Pass build settings in environment" is unchecked.)

Go to the Build Menu and click Build, or press Command+B. Xcode will invoke the Flex compiler. Build results may be viewed by clicking the right-most icon. This is where error messages will show up. See screenshots:

A successful build creates a SWF file in the ./bin/ directory of your project. 

Step 4: Run the SWF in Safari.

Drag the SWF file into a new Safari window. Your journey has just begun.

flixel Tutorials

1. Andreas Zecher's Defender clone
2. Seifer Tim's Ninja assault
3. Matthew Casperson's Lessons with Mode

Now go and make a game! :)