TweetFollow Us on Twitter

Learn F-Script in 20 Minutes

Volume Number: 23 (2007)
Issue Number: 05
Column Tag: Programming

Learn F-Script in 20 Minutes

And have fun playing with Core Image

By Philippe Mougin

Welcome

If you are a Cocoa programmer chances are that you've heard of F-Script, an open-source scripting layer dedicated to Cocoa. If you haven't tried it yet, this is your chance to learn how it can improve your productivity as well as those of the users of your own Cocoa applications. In this article, our goal will be to produce a nice little animation using fancy Core Image effects. In doing so, we will learn the basics of F-Script. So install yourself comfortably in front of your Mac, download the latest F-Script version from http://www.fscript.org and enjoy the trip!

First Contacts

We are going to learn F-Script by taking advantage of one of its key functionalities: the ability to be used interactively. With its console, you can interactively type commands in order to manipulate Objective-C objects on the fly. The F-Script console opens automatically when you launch F-Script.app. Inside it, you can type F-Script expressions or scripts and have them immediately executed when you press Return.


Figure 1. The F-Script console, waiting for your input

F-Script is a Smalltalk dialect for Cocoa and should look very familiar to you. Indeed, Brad Cox, who created objective-C describes it as "a hybrid language that contains all of C language plus major parts of Smalltalk". Here is an example of a message sending expression, both in Objective-C and F-Script. In this example, we ask for the current date using the NSDate class provided by Cocoa.

Objective-C F-Script (i.e., Smalltalk)
[NSDate date] NSDate date

As you can see, the expression is similar, except for the fact that, in F-Script, you don't have to put brackets around your message. This is because F-Script is a very simple language and sending a message is nearly the only thing you can do. Therefore, there is no need to have a special syntax to delimit messages. Now, if you type this expression in the console and hit Return, it will be immediately evaluated and the result will be displayed (obviously, the result you'll get will differ from the one shown below):

> NSDate date
2007-03-16 17:01:45 +0100

F-Script provides numerous tools to assist you during such interactive Cocoa sessions. In this first session, you are likely to find the following tips useful:

The console keeps a history of your commands. You can navigate it using the up and down arrows of your keyboard. For instance, if you mistype something and F-Script signals an error, you can use this feature to get back at your command without having to retype it.

You can insert a line break by pressing the Enter key (usually found on the numeric keypad) or by pressing Return while holding the Control key.

The console also provides a code completion mechanism that you can use by pressing the F5 key. You can then navigate between arguments placeholders with Control-Slash.

A graphical object browser opens automatically at startup. It is a very powerful tool with which you can explore objects and send them messages.

Before continuing to talk about the language itself, let me give you a little bit of the history: Smalltalk was created in the early seventies at the famous Xerox Palo Alto Research Center, the PARC, by a team led by Alan Kay. As you might know, since then, Smalltalk has been having a big influence on the software industry. For instance, you might have heard about a visit that Steve Jobs made at the PARC in 1979. A visit that had a considerable influence on the design of the Lisa and the Macintosh computers. What Steve Jobs was shown there was Smalltalk. It had a graphical interface, was the first object-oriented system, and supported networking. "You guys are sitting on a gold mine here. Why aren't you making this a product?" asked the young Steve Jobs. A short time later, several people from the PARC were working at Apple and the rest is history...

So, what is the basic concept of Smalltalk? The key insight leading to the design of Smalltalk is that we can describe everything in terms of objects. As Alan Kay puts it "Smalltalk's design is due to the insight that everything we can describe can be represented by the recursive composition of a single kind of behavioral building block that hides its combination of state and process inside itself and can be dealt with only through the exchange of messages". Indeed, in Smalltalk, everything is an object, even numbersnumbers, or booleansBooleans.

It is also important to note that F-Script provides an interactive environment with which you can directly interact with your objects, instead of having to develop a specific application each time you want to do something.

F-Script's Syntax

In a F-Script program the main control structure is message sending. In F-Script, as well as in Objective-C, a message with no argument is called a "unary message". A message with one or more colons in its selector is called a "keyword message". And, unlike Objective-C, there is a third kind of message in F-Script: a message that is composed of non-alphabetical characters like +, -, etc., is called a "binary message". A binary message always has only one argument.

Message type Objective-C F-Script
Unary [NSDate date] NSDate date
Keyword [NSDate dateWithTimeIntervalSinceNow:10] NSDate dateWithTimeIntervalSinceNow:10
Binary Not available date1 < date2

The Objective-C equivalent to date1 < date2 would be [date1 compare:date2] == NSOrderedDescending.

As in Objective-C, messages can be chained together. Expressions are evaluated from left to right, giving us the same semantics, as shown below.

Objective-C F-Script (i.e., Smalltalk)
[[NSDate date]
timeIntervalSinceNow]
NSDate date timeIntervalSinceNow

But sometimes, we need a way to determine the order of evaluation of messages. F-Script introduces a precedence rule (the only precedence rule in the language): unary messages are evaluated first, then binary messages, and then keyword messages. If you want to change the order of evaluation, you can use parenthesis to delimit a message.

The following example shows a few other differences between F-Script and Objective-C:

Objective-C F-Script (i.e., Smalltalk)
NSDate *date1 =
[NSDate date];
date1 := NSDate date.

As you see, there is no type declaration in F-Script. Everything is an object and variable need not be explicitly typed. The assignment syntax uses := instead of just = in Objective-C, and the instruction separator is not the semicolon, but the period symbol, like in English sentences. The following table shows other differences. As you can see, strings are enclosed in single quotes, and comments are enclosed in double quotes.

 
Objective-C F-Script
@"A string" 'a string'
/* A comment */ "A comment"
@selector(dateWithTimeIntervalSinceNow:) #dateWithTimeIntervalSinceNow:
[NSMutableArray arrayWithObjects:@"Hi", @"mom", nil] {'Hi', 'mom'}
NSMakePoint(200, 80) 200<>80

Displaying a picture on screen

We now know enough of F-Script to begin with our Core Image program. We will first create an NSURL object referring to the image we want to display. In this exampleexample, we will use an image that is stored on disk in the desktop picture folder. You can type the code below in the F-Script console to have it executed immediately.

imageLocation := NSURL fileURLWithPath:'
/Library/Desktop Pictures/Nature/Clown Fish.jpg'.

The imageLocation variable now points to our NSURL object. We will now create a CIImage object, initialized with our image on-disk.

image := CIImage imageWithContentsOfURL:imageLocation.

Note that we are using standard methods provided by the Mac OS X frameworks. Now that we have an image object, we can ask it to draw itself on screen, again using a standard method.

image drawInRect:(200<>80 extent:300<>200) 
fromRect:image extent operation:NSCompositeSourceOver fraction:1.

After executing this code, we should see a beautiful little image displayed in the console, as shown below.


Figure 2. Loading and displaying an image using Core Image and F-Script

The first argument passed to the drawing method is the rectangle we want to draw in, which is denoted with 200<>80 extent:300<>200. This expression actually creates an NSValue object representing a rectangle with an origin at (200, 80), a width of 300 and a height of 200. When passed to the method, the NSValue is automatically mapped by F-Script to an NSRect structure. This kind of automatic mapping between objects and primitives Objective-C types makes it possible to use the Mac OS X Objective-C based frameworks from a pure object language such as F-Script. You can change the rectangle size to make the image bigger or smaller and immediately see the result on-screen.

The drawing method draws the image in the current graphic context, which, in our example, happens to be the F-Script console. It is possible, of course, to draw elsewhere, using standard Mac OS X techniques.

Using core image filters

Core Image filters allow us to do all kind of highly optimized image processing. Mac OS X comes bundled with dozens of filters. Going forward with our exploration, we will apply a filter known as CIBumpDistortion, which creates a bump in the image. You are encouraged to try other filters as well. F-Script's interactivity makes it fun and efficient to explore such Mac OS X capabilities. The following F-Script code creates a CIBumpDistortion filter object and configures it to process our image, creating a bump of radius to 800 and of scale 2.

filter := CIFilter filterWithName:'CIBumpDistortion'.
filter setValue:image forKey:'inputImage'.
filter setValue:(CIVector vectorWithX:1000 Y:700) forKey:'inputCenter'.
filter setValue:900 forKey:'inputRadius'.
filter setValue:1 forKey:'inputScale'.

Now that the filter is configured, it will apply itself to our image when asked to provides its output, creating a new image and giving it back to us:

bumpedImage := filter valueForKey:'outputImage'.

We can now draw this new image on screen:

bumpedImage drawInRect:(200<>80 extent:300<>200) 
fromRect:image extent operation:NSCompositeSourceOver fraction:1.


Figure 3. Our image after processing by a Core Image "bump" filter

To understand how the filter works, it is interesting to change its configuration (for instance, the values of its radius and its scale) and to regenerate and redisplay the image. If you are sitting behind an F-Script console, you are encouraged to do so!

Using blocks to create an animation

Now that we know how to process and display an image, we can create a nice little animation by repeatedly processing the image with a varying filter and displaying the result. To do that we just need to learn how write a loop using F-Script.

But, wait a minute... Isn't F-Script supposed to have a very simple syntax, where everything is expressed by sending messages to objects? Well, this is exact and, in fact, F-Script does not have any special syntax for control structures such as loops or conditionals. So the question here is "How can we express useful programs without such syntax?" To answer that, let me introduce you to the concept of code blocks in F-Script. Below, we see a code block in Objective-C and one in F-Script. Note the use of brackets in F-Script, instead of curly braces.

Objective-C F-Script (i.e., Smalltalk)
{
instruction1;
instruction2;
}
[
instruction1.
instruction2.
]

The code blocks look similar, but the way they work is quite different. In Objective-C, when the computer executes the code block, it simply executes the instructions in it immediately. In F-Script, the code block is actually a kind of literal notation for an object that contains the instructions. In other words, a block represents a deferred sequence of actions. In F-Script, the presence of a code block does not lead to the execution of its content, but to the creation of a block object, that can then be asked to execute the instructions. To do that, we send the "value" message to the block. The result returned by the execution of a block is the result of the evaluation of its last instruction.

As you can see below, F-Script blocks can have local variables, just like in Objective-C. If the instructions in the block refer to a variable that is not declared as local, F-Script will look for it in the enclosing lexical context of the block, as is the case in Objective-C.

Objective-C F-Script (i.e., Smalltalk)
{
id local1,local2;

instruction1;
instruction2;
}
[
|local1 local2|

instruction1.
instruction2.
]

The main point to understand here is that F-Script blocks are objects. Like with any object, you can send messages to a block, you can assign a block to a variable, store a block in a collection, pass a block as an argument to a method, archive a block on-disk, and so on. Blocks are not unique to F-Script (or Smalltalk). They are present in numerous languages (sometimes under the name of "closure" or "lambda expressions") such as Ruby, Python, Lisp, GroovyGroovy, and the forthcoming C# 3.

Now that we have blocks, it is easy to do conditional evaluation. Boolean objects provide a method named ifTrue: which takes a block as argument. If the value of the Boolean is true, then the block is executed by the method.

Objective-C F-Script (i.e., Smalltalk)
if (a > b) 
{
instructions
}
(a > b) ifTrue:
[
instructions
]

Boolean objects also have a method named ifTrue:ifFalse: that lets you have something equivalent to the if/else control structure of Objective-C. This method takes two blocks as arguments. One that gets executed if the booleanBoolean is true and the other one that gets executed if the booleanBoolean is false.

Objective-C F-Script
if (a > b) 
{
  instructions
}
else
{
  instructions
}
(a > b) ifTrue:
[
  instructions
]
ifFalse:
[
  instructions
]	

For performing our animation, we need a way to repeatedly evaluate a block. Let's review how F-Script provides this.

Blocks provide a method named whileTrue:, which takes another block as argument. The receiver of the whileTrue: message evaluates itself, and, if the result of this evaluation is a booleanBoolean with a value of true, the argument gets evaluated. This process is repeated as long as the receiver evaluates to true.+

Note that in the example with conditionals, the ifTrue: message was sent to a booleanBoolean object. In the latest example, the whileTrue: message is sent to a block that returns a booleanBoolean. This is very different. Indeed, it would not make sense to implement a whileTrue: method in the booleanBoolean class. This is because the value of a particular booleanBoolean never changes; whereas the value returned by the evaluation of a block can change from one evaluation to another.

Now that we know how to express repetitive evaluation, we can finally write our animation:

keyWindow := NSApplication sharedApplication keyWindow.
rect := (200<>100 extent:300<>200).
i := 0.
[i < 2500] whileTrue:
[
    filter setValue:(CIVector vectorWithX:i Y:700) forKey:'inputCenter'.
    bumpedImage := filter valueForKey:'outputImage'.
    bumpedImage drawInRect:rect fromRect:image extent ¬ 
    operation:NSCompositeSourceOver fraction:1.
    keyWindow flushWindow.
    i := i + 5.
]

As you can see, we move the bump across the image, by varying the X component of the CIVector object that define the center of the bump. We use a control variable named "i" that we increment by five at each iteration of our loop until it becomes equal to 2500. We also ask the window to flush itself at each step of our iteration in order to display the new image and produce the animation effect.

Blocks with arguments

For such kind of iteration, however, a for loop is more appropriate, and you might wonder if F-Script provides it. Well, it does! But in order to master it we must learn another feature of blocks: support for arguments. Block arguments are declared at the beginning of the block, just after the opening bracket. Each argument name is specified after a colon and a vertical bar ends the argument list. A block must then be executed using an appropriate "value..." message. For example, here is a block with no argument. We evaluate it by sending it the value message.

['hello world'] value      returns       'hello world'

Below is a block with one argument. In this case, we send a value: message, specifying the argument that will be passed to the block.

[:a| a class] value:'a string'      returns       String

Here is a block with two arguments. To evaluate it, we send it a value:value: message.

[:a :b| a + b] value:2 value:3      returns       5

Now that we have blocks with arguments, we can make use of powerful methods. For example, numbers have a method named to:do: which takes an number and a block as arguments. The block is evaluated for each integer between the receiver and the first argument (both included).

Objective-C F-Script
for (int i=0; i <= 100; i++) 
{
  instructions using i
}
 0 to:100 do:
[:i|
  instructions using i
]	

F-Script also provides a to:by:do: method that let us specify an iteration step.

Objective-C F-Script
for (int i=0; i <= 100; i = i + 5) 
{
  instructions using i
}
0 to:100 by:5 do:
[:i|
  instructions using i
] 

We can make use of it in our animation script, which then becomes:

keyWindow := NSApplication sharedApplication keyWindow.
rect := (200<>100 extent:300<>200).
0 to:2500 by:5 do:
[:i|
    filter setValue:(CIVector vectorWithX:i Y:700) forKey:'inputCenter'.
    bumpedImage := filter valueForKey:'outputImage'.
    bumpedImage drawInRect:rect fromRect:image extent 
operation:NSCompositeSourceOver fraction:1.
    keyWindow flushWindow.
]

You can change the value of the step to see how it makes the animation faster or slower.

Conclusion

Now that you are familiar with F-Script, you can use it whenever you want to explore a new Objective-C API, interactively prototype code or debug an application. And since you can easily embed it into your own application, you can provide your users with an interactive and scripting layer for your application's functionalities, by just exposing them as Objective-C objects.


Philippe Mougin is the creator of F-Script. He works at OCTO Technology, a French consulting company, where he explores and promotes the use of dynamic languages in enterprise systems. You can reach him at pmougin@acm.org.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

iMazing 2.9.4 - Complete iOS device mana...
iMazing (was DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and from... Read more
BBEdit 12.6.2 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
Final Cut Pro X 10.4.6 - Professional vi...
Final Cut Pro X is a professional video editing solution. Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Compressor 4.4.4 - Adds power and flexib...
Compressor adds power and flexibility to Final Cut Pro X export. Customize output settings, work faster with distributed encoding, and tap into a comprehensive set of delivery features. Features... Read more
Apple iMovie 10.1.11 - Edit personal vid...
With an all-new design, Apple iMovie lets you enjoy your videos like never before. Browse your clips more easily, instantly share your favorite moments, and create beautiful HD movies and Hollywood-... Read more
Motion 5.4.3 - Create and customize Fina...
Motion is designed for video editors, Motion 5 lets you customize Final Cut Pro titles, transitions, and effects. Or create your own dazzling animations in 2D or 3D space, with real-time feedback as... Read more
Parallels Desktop 14.1.3 - Run Windows a...
Parallels allows you to run Windows and Mac applications side by side. Choose your view to make Windows invisible while still using its applications, or keep the familiar Windows background and... Read more
ffWorks 1.2 - Convert multimedia files b...
ffWorks, focused on simplicity, brings a fresh approach to the use of FFmpeg, allowing you to create ultra-high-quality movies without the need to write a single line of code on the command-line.... Read more
CleanMyMac X 4.3.0.3 - Delete files that...
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
EtreCheck Pro 5.2 - For troubleshooting...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more

Latest Forum Discussions

See All

Call of Duty Mobile - Three other Activi...
This week Activision has revealed that Call of Duty Mobile is real, it's coming soon, and it looks pretty awesome. We got all of that from a trailer, but it also got us thinking about what other Activision games we'd like to see coming to mobile.... | Read more »
The best shooters on iOS
In case you missed it yesterday, Tencent and Activision announced they are putting out a new Call of Duty game for mobile. While details are pretty scant, they did put out a trailer (see above) and have a page where you can pre-register for the... | Read more »
The best games for iPhone - The definiti...
Hi there, and welcome to our ever-increasing list of the very best games for iPhone. We're going to be updating this regularly with new content, so make sure you check back often, because you're not going to want to miss out on even one of the... | Read more »
Everything you need to know to win in Sp...
Sure, Sprout: Idle Garden might be an idle game (we know, we know, it was pretty obvious from the name), but that doesn't mean there aren't plenty of hints and tips you can exploit to make sure you're getting the best possible return from your... | Read more »
Huge new update for fantasy RPG Final Bl...
The hit fantasy RPG Final Blade arrived on western shores last month to much acclaim, thanks in large part to its successful mix of vibrant visuals, rich storytelling, and classic RPG mechanics. Now, the game is set to receive a whopping new update... | Read more »
Everything you need to know to win in Pe...
Pet Rescue Puzzle Saga is the latest game in King's long line of sagas. It's a match-stuff puzzler, as you might expect, but it's got a few new twists on the already established formula that, while they do keep things fresh, are likely to come as... | Read more »
REKT! guide - Is the latest content upda...
When REKT! first came out, I was impressed with the game’s ability to channel the gameplay of Tony Hawk’s Pro Skater in a small, streamlined package. Be that as it may, I was also pretty underwhelmed with the game’s lack of content. | Read more »
The best games for iPhone and iPad that...
Just like every Thursday, today we're taking some time to let you know what we think are the best games that have come out over the past week. We've had hands-on time with all of them, so you can trust us when we tell you that we're pretty clued... | Read more »
Mobile games you probably haven't p...
The App Store is bursting at the seams with all kinds of apps and games of varying quality, but one of the most consistent issues with it is discoverability. Despite having what seems like unlimited money and a full App Store editorial team, Apple... | Read more »
Get gorgeous characters and new skins in...
NetEase Games’s Onmyoji is reaching the last part of the crossover event with the classic anime Inuyasha. Once the maintenance on March13th is over you’ll be able to get Inuyasha, Sesshomaru, and Kikyo. You can get hold of these through any summon... | Read more »

Price Scanner via MacPrices.net

Deal Alert! High-end 13″ 2.3GHz Quad-Core Mac...
Amazon has the high-end 2018 13″ 2.3GHz/512GB Space Gray Quad-Core Touch Bar MacBook Pro (MR9R2LL/A) on sale for $1699.99 shipped. That’s $300 off Apple’s MSRP for this model. This is the same... Read more
New 2019 21″ 3.6GHz Quad-Core iMac already on...
B&H Photo has the new 2019 21″ 3.6GHz Quad-Core 4K iMac on sale, for preorder, for $1099 including free next day shipping (when it arrives). That’s $200 off Apple’s MSRP for this brand new iMac,... Read more
Apple has 13″ 2.3GHz Quad-Core MacBook Pros a...
Apple has Certified Refurbished 2018 13″ 2.3GHz 4-Core Touch Bar MacBook Pros available for $270-$300 off the cost of new models, with prices starting at $1529. Apple’s one-year warranty is included... Read more
Amazon continues to offer the lowest prices o...
Amazon is offering new 9.7″ WiFi iPads with Apple Pencil Support for $50-$100 off MSRP today, with prices starting at only $249. These are the same iPads found in Apple’s retail and online stores: –... Read more
Get a new 2018 Mac mini for $50-$100 off Appl...
Apple resellers are offering new 2018 4-Core and 6-Core Mac minis for $50-$100 off MSRP for a limited time. B&H Photo has the new 2018 4-Core and 6-Core Mac minis on sale for $50-$100 off Apple’s... Read more
Apple resellers drop prices on clearance 21″...
B&H Photo has dropped prices on clearance, previous-generation, 21″ and 27″ 5K Apple iMacs by up to $300 off original MSRP. These are the same models offered by Apple in their retail and online... Read more
Preorder Apple’s new 2019 AirPods for up to $...
Apple today introduced new second-generation AirPods featuring 50% more talk time, hands-free “Hey Siri” capability, and an optional wireless charging case (also compatible with first-generation... Read more
12″ 1.2GHz MacBooks on sale for $100-$300 off...
B&H Photo has new 2017 12″ 1.2GHz MacBooks on sale for $100-$300 off MSRP today. Shipping is free: – 12″ 1.2GHz Space Gray MacBook: $1199 $100 off MSRP – 12″ 1.2GHz Silver MacBook: $1199 $100 off... Read more
Learn Key Vocabulary Before Upgrading A Mac W...
FEATURE: 03.20.19- It’s the first day of Spring and in addition to sprucing things up around one’s living quarters, Mac users may be thinking about doing the same with their computers but whether... Read more
Apple drops prices on clearance refurbished 4...
Apple has dropped prices on Certified Refurbished 2017 21″ 4K & 27″ 5K iMacs with models now available starting at $1059. Apple’s one-year warranty is standard, shipping is free, and each iMac... Read more

Jobs Board

Student Employment - *Apple* Campus Rep - S...
The people here at Apple don't just create products - they create the kind of wonder that's revolutionized entire industries. It's the diversity of those people and Read more
*Apple* /MAC Support Technician - AECOM (Unit...
…DC, Washington, DC **Job Summary** AECOM has an immediate opportunity for an Apple Support Engineer to support a government agency's capabilities in Washington, DC Read more
*Apple* Certified and Windows Desktop Suppor...
** Apple Certified and Windows Desktop Support Engineer** **Preferred Qualifications** **About the team ** The Desktop Support Team is a fast paced, service oriented Read more
Geek Squad *Apple* Master Consultation Agen...
**680306BR** **Job Title:** Geek Squad Apple Master Consultation Agent **Job Category:** Services/Installation/Repair **Location Number:** 001540-Tuscaloosa-Store Read more
Best Buy *Apple* Computing Master - Best Bu...
**680138BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Location Number:** 000316-75Th& Lemont-Store **Job Description:** **What does a Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.