Pure Mac: Messaging
Founded in 2011, Zoom is the leader in modern enterprise video communications, with a secure, easy platform for video and audio conferencing, messaging, and webinars across mobile, desktop, and room systems. Jul 30, 2018 - Google blasts you with Windows and Mac error messages in new. The strength of Chrome OS is its pure simplicity, and that's not necessarily. Pure Football. For those of you who ONLY want to talk about SAFC and football. All off topic threads will be deleted.
Smalltalk-80 version 2 / 1980; 38 years ago ( 1980), (multi-platform) Major, Smalltalk/X, Influenced by, Influenced, Lisaac, 5,. at Wikibooks Smalltalk is an,. Smalltalk was created as the language to underpin the 'new world' of computing exemplified by 'human–computer symbiosis'.
It was designed and created in part for use, more so for, at the Learning Research Group (LRG) of by, Ted Kaehler, Scott Wallace, and others during the 1970s. The language was first generally released as Smalltalk-80. Smalltalk-like languages are in continuing active development and have gathered loyal communities of users around them.
ANSI Smalltalk was ratified in 1998 and represents the standard version of Smalltalk. Smalltalk took second place for 'most loved programming language' in the Developer Survey in 2017, but it was not among the 26 most loved programming languages of the 2018 survey. Contents. History There are a large number of Smalltalk variants. The unqualified word Smalltalk is often used to indicate the Smalltalk-80 language, the first version to be made publicly available and created in 1980.
Smalltalk was the product of research led by at (PARC); Alan Kay designed most of the early Smalltalk versions, wrote most of the documentation, and implemented most of the early versions. The first version, termed Smalltalk-71, was created by Kay in a few mornings on a bet that a programming language based on the idea of inspired by could be implemented in 'a page of code'. A later variant used for research work is now termed Smalltalk-72 and influenced the development of the. Its were very different from modern Smalltalk variants. After significant revisions which froze some aspects of execution semantics to gain performance (by adopting a -like class model of execution), Smalltalk-76 was created. This system had a featuring most of the now familiar tools, including a class library code browser/editor.
Smalltalk-80 added, to help maintain the 'everything is an object' (except private instance variables) paradigm by associating properties and behavior with individual classes, and even primitives such as integer and boolean values (for example, to support different ways to create instances). Smalltalk-80 was the first language variant made available outside of PARC, first as Smalltalk-80 Version 1, given to a small number of firms (, and (DEC)) and universities for and implementing on their platforms. Later (in 1983) a general availability implementation, named Smalltalk-80 Version 2, was released as an image (platform-independent file with object definitions) and a specification.
ANSI Smalltalk has been the standard language reference since 1998. Two of the currently popular Smalltalk implementation variants are descendants of those original Smalltalk-80 images. Is an implementation derived from Smalltalk-80 Version 1 by way of Apple Smalltalk. Is derived from Smalltalk-80 version 2 by way of Smalltalk-80 2.5 and ObjectWorks (both products of ParcPlace Systems, a Xerox PARC spin-off company formed to bring Smalltalk to the market). As an interesting link between generations, in 2001 Vassili Bykov implemented Hobbes, a virtual machine running Smalltalk-80 inside VisualWorks. ( later ported Hobbes to Squeak.) During the late 1980s to mid-1990s, Smalltalk environments—including support, training and add-ons—were sold by two competing organizations: ParcPlace Systems and Digitalk, both California based.
ParcPlace Systems tended to focus on the Unix/Sun microsystems market, while Digitalk focused on Intel-based PCs running Microsoft Windows or IBM's OS/2. Both firms struggled to take Smalltalk mainstream due to Smalltalk's substantial memory needs, limited run-time performance, and initial lack of supported connectivity to -based relational database servers.
While the high price of ParcPlace Smalltalk limited its market penetration to mid-sized and large commercial organizations, the Digitalk products initially tried to reach a wider audience with a lower price. IBM initially supported the Digitalk product, but then entered the market with a Smalltalk product in 1995 called VisualAge/Smalltalk. Easel introduced Enfin at this time on Windows and OS/2. Enfin became far more popular in Europe, as IBM introduced it into IT shops before their development of IBM Smalltalk (later VisualAge). Enfin was later acquired by, and is now sold under the name, and is part of the Cincom Smalltalk product suite. In 1995, ParcPlace and Digitalk merged into ParcPlace-Digitalk and then rebranded in 1997 as ObjectShare, located in Irvine, CA.
ObjectShare (: OBJS) was traded publicly until 1999, when it was delisted and dissolved. The merged firm never managed to find an effective response to Java as to market positioning, and by 1997 its owners were looking to sell the business. In 1999, Seagull Software acquired the ObjectShare Java development lab (including the original Smalltalk/V and Visual Smalltalk development team), and still owns VisualSmalltalk, although worldwide distribution rights for the Smalltalk product remained with ObjectShare who then sold them to. VisualWorks was sold to and is now part of Cincom Smalltalk. Cincom has backed Smalltalk strongly, releasing multiple new versions of VisualWorks and ObjectStudio each year since 1999., and Object Arts, plus other vendors continue to sell Smalltalk environments. IBM has 'end of life'd VisualAge Smalltalk having in the late 1990s decided to back Java and it is, as of 2006, supported by Instantiations, Inc.
Which has renamed the product VA Smalltalk and released several new versions. The open implementation has an active community of developers, including many of the original Smalltalk community, and has recently been used to provide the Etoys environment on the project, a toolkit for developing collaborative applications, and the virtual world application. Is a implementation of a derivative of Smalltalk-80 from the project. Smalltalk is a fork of oriented toward research and use in commercial environments. A significant development, that has spread across all Smalltalk environments as of 2016, is the increasing usage of two web frameworks, and, to simplify the building of complex web applications. Seaside has seen considerable market interest with Cincom, Gemstone, and Instantiations incorporating and extending it.
Influences Smalltalk was one of many object-oriented programming languages based on. Smalltalk is also one of the most influential programming languages. Virtually all of the object-oriented languages that came after—, and many others—were influenced by Smalltalk.
Smalltalk was also one of the most popular languages with the, and communities. The highly productive environment provided by Smalltalk platforms made them ideal for rapid, iterative development.
Smalltalk emerged from a larger program of funded research that in many ways defined the modern world of computing. In addition to Smalltalk, working prototypes of things such as, GUIs, the mouse, and the Internet were developed by ARPA researchers in the 1960s. Alan Kay (one of the inventors of Smalltalk) also described a tablet computer he called the which resembles modern tablet computers like the iPad. Smalltalk environments were often the first to develop what are now common object-oriented software design patterns. One of the most popular is the (MVC) pattern for design. The MVC pattern enables developers to have multiple consistent views of the same underlying data.
It's ideal for software development environments, where there are various views (e.g., entity-relation, dataflow, object model, etc.) of the same underlying specification. Also, for simulations or games where the underlying model may be viewed from various angles and levels of abstraction.
In addition to the MVC pattern, the Smalltalk language and environment were highly influential in the history of the (GUI) and the what you see is what you get user interface, font editors, and desktop metaphors for UI design. The powerful built-in debugging and object inspection tools that came with Smalltalk environments set the standard for all the, starting with environments, that came after. Object-oriented programming. Main article: As in other object-oriented languages, the central concept in Smalltalk-80 (but not in Smalltalk-72) is that of an object. An object is always an instance of a class.
Classes are 'blueprints' that describe the properties and behavior of their instances. For example, a GUI's window class might declare that windows have properties such as the label, the position and whether the window is visible or not. The class might also declare that instances support operations such as opening, closing, moving and hiding. Each particular window object would have its own values of those properties, and each of them would be able to perform operations defined by its class. A Smalltalk object can do exactly three things:. Hold state (references to other objects).
from itself or another object. In the course of processing a message, send messages to itself or another object.
The state an object holds is always private to that object. Other objects can query or change that state only by sending requests (messages) to the object to do so. Any message can be sent to any object: when a message is received, the receiver determines whether that message is appropriate.
Alan Kay has commented that despite the attention given to objects, messaging is the most important concept in Smalltalk: 'The big idea is 'messaging'—that is what the kernel of Smalltalk/Squeak is all about (and it's something that was never quite completed in our Xerox PARC phase).' Smalltalk is a 'pure' object-oriented programming language, meaning that, unlike and, there is no difference between values which are objects and values which are primitive types. In Smalltalk, primitive values such as integers, booleans and characters are also objects, in the sense that they are instances of corresponding classes, and operations on them are invoked by sending messages.
A programmer can change or extend (through ) the classes that implement primitive values, so that new behavior can be defined for their instances—for example, to implement new control structures—or even so that their existing behavior will be changed. This fact is summarized in the commonly heard phrase 'In Smalltalk everything is an object', which may be more accurately expressed as 'all values are objects', as variables are not. Since all values are objects, are also objects. Each class is an instance of the of that class. Metaclasses in turn are also objects, and are all instances of a class called Metaclass. —Smalltalk's way of expressing —are also objects.
Reflection is a term that computer scientists apply to software programs that have the ability to inspect their own structure, for example their or of input and output parameters. Reflection was first primarily a feature of interpreted languages such as Smalltalk and Lisp. Statements being interpreted means that the programs have access to information created as they were parsed and can often even modify their own structure. Reflection is also a feature of having a meta-model as Smalltalk does. The meta-model is the model that describes the language, and developers can use the meta-model to do things like walk through, examine, and modify the parse tree of an object.
Or find all the instances of a certain kind of structure (e.g., all instances of the Method class in the meta-model). Smalltalk-80 is a totally reflective system, implemented in Smalltalk-80. Smalltalk-80 provides both structural and computational reflection. Smalltalk is a structurally reflective system which structure is defined by Smalltalk-80 objects. The classes and methods that define the system are also objects and fully part of the system that they help define.
The Smalltalk compiler compiles textual source code into method objects, typically instances of CompiledMethod. These get added to classes by storing them in a class's method dictionary. The part of the class hierarchy that defines classes can add new classes to the system. The system is extended by running Smalltalk-80 code that creates or defines classes and methods.
In this way a Smalltalk-80 system is a 'living' system, carrying around the ability to extend itself at run time. Since the classes are objects, they can be asked questions such as 'what methods do you implement?' Or 'what fields/slots/instance variables do you define?'
So objects can easily be inspected, copied, (de) and so on with generic code that applies to any object in the system. Smalltalk-80 also provides computational reflection, the ability to observe the computational state of the system. In languages derived from the original Smalltalk-80 the current activation of a method is accessible as an object named via a pseudo-variable (one of the six reserved words), thisContext. By sending messages to thisContext a method activation can ask questions like 'who sent this message to me'. These facilities make it possible to implement or -like back-tracking without modifying the virtual machine. The exception system is implemented using this facility. One of the more interesting uses of this is in the web framework which relieves the programmer of dealing with the complexity of a Web Browser's back button by storing continuations for each edited page and switching between them as the user navigates a web site.
Bigasoft VOB Converter is suited for both experts and beginners you can complete your converting as easy as 1-2-3. Bigasoft VOB Converter helps you extract sound tracks from video clips with ease. Save time With the power of preview before converting and batch converting DVD chapters or titles at a time, the VOB file converter can fast convert DVD for saving your time. Only 3 easy steps Simply open DVD, select profile and press the Start button, it’s that simple. Coupon bigasoft asf converter for mac. Enjoy DVD music How many times have you watched DVD movie with a fantastic piece of music on it?
Programming the web server using Seaside can then be done using a more conventional programming style. An example of how Smalltalk can use reflection is the mechanism for handling errors. When an object is sent a message that it does not implement, the virtual machine sends the object the doesNotUnderstand: message with a of the message as an argument.
The message (another object, an instance of Message) contains the selector of the message and an Array of its arguments. In an interactive Smalltalk system the default implementation of doesNotUnderstand: is one that opens an error window (a Notifier) reporting the error to the user. Through this and the reflective facilities the user can examine the context in which the error occurred, redefine the offending code, and continue, all within the system, using Smalltalk-80's reflective facilities. By creating a class that understands (implements) only doesNotUnderstand:, one can create an instance that can intercept any message sent to it via its doesNotUnderstand: method. Such instances are called transparent proxies.
Such proxies can then be used to implement a number of facilities such as distributed Smalltalk where messages are exchanged between multiple Smalltalk systems, database interfaces where objects are transparently faulted out of a database, etc. The design of distributed Smalltalk influenced such systems as. This section needs additional citations for. Unsourced material may be challenged and removed. (June 2014) Smalltalk-80 syntax is rather minimalist, based on only a handful of declarations and reserved words.
In fact, only six 'keywords' are reserved in Smalltalk: true, false, nil, self, super, and thisContext. These are properly termed pseudo-variables, identifiers that follow the rules for variable identifiers but denote bindings that a programmer cannot change. The true, false, and nil pseudo-variables are instances. Self and super refer to the receiver of a message within a method activated in response to that message, but sends to super are looked up in the superclass of the method's defining class rather than the class of the receiver, which allows methods in subclasses to invoke methods of the same name in superclasses. ThisContext refers to the current activation record. The only built-in language constructs are message sends, assignment, method return and literal syntax for some objects. From its origins as a language for children of all ages, standard Smalltalk syntax uses punctuation in a manner more like English than mainstream coding languages.
The remainder of the language, including control structures for conditional evaluation and iteration, is implemented on top of the built-in constructs by the standard Smalltalk class library. (For performance reasons, implementations may recognize and treat as special some of those messages; however, this is only an optimization and is not hardwired into the language syntax.) The adage that 'Smalltalk syntax fits on a ' refers to a code snippet by, demonstrating all the basic standard syntactic elements of methods. 'I said, 'Hello, world!' Two equal strings (strings are equal if they contain all the same characters) can be different objects residing in different places in memory. In addition to strings, Smalltalk has a class of character sequence objects called Symbol. Symbols are guaranteed to be unique—there can be no two equal symbols which are different objects. Because of that, symbols are very cheap to compare and are often used for language artifacts such as message selectors (see below).
Symbols are written as # followed by a. Some smalltalk code. Blocks are explained in detail further in the text. Many Smalltalk dialects implement additional syntaxes for other objects, but the ones above are the essentials supported by all. Variable declarations The two kinds of variables commonly used in Smalltalk are instance variables and temporary variables.
Other variables and related terminology depend on the particular implementation. For example, has class shared variables and namespace shared variables, while and many other implementations have class variables, pool variables and global variables. Temporary variable declarations in Smalltalk are variables declared inside a method (see below). They are declared at the top of the method as names separated by spaces and enclosed by vertical bars.
Vowels:= 'aeiou' Assigns the string 'aeiou' to the formerly declared vowels variable. The string is an object (a sequence of characters between single quotes is the syntax for literal strings), created by the compiler at compile time. In the original Parc Place image, the glyph of the underscore character ⟨⟩ appeared as a left-facing arrow ⟨←⟩ (like in the 1963 version of the code). Smalltalk originally accepted this left-arrow as the only assignment operator.
Some modern code still contains what appear to be underscores acting as assignments, hearkening back to this original usage. Most modern Smalltalk implementations accept either the underscore or the colon-equals syntax. Messages The message is the most fundamental language construct in Smalltalk.
Even control structures are implemented as. Smalltalk adopts by default a synchronous, single strategy (as contrasted to the asynchronous, strategy adopted by some other object-oriented languages).
The following example sends the message 'factorial' to number 42. 3 4 is the message ' sent to 3 with argument 4 (the answer of which will be false). Notice, that the Smalltalk-80 language itself does not imply the meaning of those operators. The outcome of the above is only defined by how the receiver of the message (in this case a Number instance) responds to messages '+' and '. A side effect of this mechanism is operator overloading.
A message ' can also be understood by other objects, allowing the use of expressions of the form 'a b' to compare them. Expressions An expression can include multiple message sends. In this case expressions are parsed according to a simple order of precedence. Unary messages have the highest precedence, followed by binary messages, followed by keyword messages. ( 3 factorial + 4) factorial between: 10 and: 100 will change the meaning so that the expression first computes '3 factorial + 4' yielding 10. That 10 then receives the second 'factorial' message, yielding 3628800.
3628800 then receives 'between:and:', answering false. Note that because the meaning of binary messages is not hardwired into Smalltalk-80 syntax, all of them are considered to have equal precedence and are evaluated simply from left to right. Because of this, the meaning of Smalltalk expressions using binary messages can be different from their 'traditional' interpretation. PositiveAmounts:= allAmounts select: : anAmount anAmount isPositive Note that this is related to, wherein patterns of computation (here selection) are into. For example, the message select: on a Collection is equivalent to the higher-order function on an appropriate. Control structures Control structures do not have special syntax in Smalltalk. They are instead implemented as messages sent to objects.
For example, conditional execution is implemented by sending the message ifTrue: to a Boolean object, passing as an argument the block of code to be executed if and only if the Boolean receiver is true. The following code demonstrates this. aString vowels aString:= 'This is a string'.
Vowels:= aString select: : aCharacter aCharacter isVowel. In the last line, the string is sent the message select: with an argument that is a code block literal. The code block literal will be used as a predicate function that should answer true if and only if an element of the String should be included in the Collection of characters that satisfy the test represented by the code block that is the argument to the 'select:' message.
A String object responds to the 'select:' message by iterating through its members (by sending itself the message 'do:'), evaluating the selection block ('aBlock') once with each character it contains as the argument. When evaluated (by being sent the message 'value: each'), the selection block (referenced by the parameter 'aBlock', and defined by the block literal ':aCharacter aCharacter isVowel'), answers a boolean, which is then sent 'ifTrue:'. If the boolean is the object true, the character is added to a string to be returned. Because the 'select:' method is defined in the abstract class Collection, it can also be used like this. Object subclass: #MessagePublisher instanceVariableNames: ' classVariableNames: ' poolDictionaries: ' category: 'Smalltalk Examples' Often, most of this definition will be filled in by the environment. Notice that this is a message to the Object class to create a subclass called MessagePublisher. In other words: classes are in Smalltalk which can receive messages just like any other object and can be created dynamically at execution time.
Methods When an object receives a message, a method matching the message name is invoked. The following code defines a method publish, and so defines what will happen when this object receives the 'publish' message. MessagePublisher new publish Hello World example The is used by virtually all texts to new programming languages as the first program learned to show the most basic syntax and environment of the language.
For Smalltalk, the program is extremely simple to write. The following code, the message 'show:' is sent to the object 'Transcript' with the String literal 'Hello, world!' As its argument. Invocation of the 'show:' method causes the characters of its argument (the String literal 'Hello, world!' ) to be displayed in the transcript ('terminal') window. Transcript show: 'Hello, world!'
Note that a Transcript window would need to be open in order to see the results of this example. Image-based persistence Most popular programming systems separate static program code (in the form of class definitions, functions or procedures) from dynamic, or, program state (such as objects or other forms of program data). They load program code when a program starts, and any prior program state must be recreated explicitly from configuration files or other data sources. Any settings the program (and programmer) does not explicitly save must be set up again for each restart. A traditional program also loses much useful document information each time a program saves a file, quits, and reloads. This loses details such as undo history or cursor position. Image based systems don't force losing all that just because a computer is turned off, or an OS updates.
Many Smalltalk systems, however, do not differentiate between program data (objects) and code (classes). In fact, classes are objects. Thus, most Smalltalk systems store the entire program state (including both Class and non-Class objects) in an file.
The image can then be loaded by the Smalltalk to restore a Smalltalk-like system to a prior state. This was inspired by FLEX, a language created by and described in his M.Sc. Smalltalk images are similar to (restartable) and can provide the same functionality as core dumps, such as delayed or remote debugging with full access to the program state at the time of error. Other languages that model application code as a form of data, such as, often use image-based persistence as well.
This method of persistence is powerful for rapid development because all the development information (e.g. Parse trees of the program) is saved which facilitates debugging. However, it also has serious drawbacks as a true persistence mechanism. For one thing, developers may often want to hide implementation details and not make them available in a run time environment. For reasons of legality and maintenance, allowing anyone to modify a program at run time inevitably introduces complexity and potential errors that would not be possible with a compiled system that exposes no source code in the run time environment. Also, while the persistence mechanism is easy to use, it lacks the true persistence abilities needed for most multi-user systems.
The most obvious is the ability to do transactions with multiple users accessing the same database in parallel. Level of access Everything in Smalltalk-80 is available for modification from within a running program. This means that, for example, the can be changed in a running system without restarting it.
Pure Mac Downloads
In some implementations, the syntax of the language or the implementation can also be changed on the fly. Even the statement true become: false is valid in Smalltalk, although executing it is not recommended.
Pure Mac: Messaging System
Just-in-time compilation.
Comments are closed.