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39-492: M-expressions are a syntax for LISP code and provide function notation , syntax for a cond form and for embedded literal data (via S-expressions) into programs. Thus M-Expressions used S-Expressions for literal data. The syntax for S-Expressions ("The Data Language") and M-Expressions ("The Meta Language") is defined on pages 8 and 9 of the Lisp 1.5 manual. M-Expressions also had a corresponding S-Expression representation. Code

78-491: A bolt on feature that invariably causes problems and adds syntax. Under Dylan, every function call can be simply placed in the "Private" or "Development" interface, and collect up publicly accessible functions in Public . Under Java or C++ the visibility of an object is defined in the code, meaning that to support a similar change, a programmer would be forced to rewrite the definitions fully, and could not have two versions at

117-466: A module defines a namespace. Classes can be placed together in modules, or cut across them, as the programmer wishes. Often the complete definition for a class does not exist in a single module, but is spread across several that are optionally collected together. Different programs can have different definitions of the same class, including only what they need. For example, consider an add-on library for regex support on String . In some languages, for

156-504: A part of String ; instead, it is isolated in its own set of functions that must be called separately. Instead of myString.parseWith(myPattern) , which would be the natural organization from an OO viewpoint, something like myPattern.parseString(myString) is used, which effectively reverses the ordering. Under Dylan, many interfaces can be defined for the same code, for instance the String concatenation method could be placed in both

195-420: A continuum between dynamic and static programming and supporting evolutionary development (allowing for rapid prototyping followed by incremental refinement and optimization). Dylan's main design goal is to be a dynamic language well-suited for developing commercial software . Dylan attempts to address potential performance issues by introducing "natural" limits to the full flexibility of Lisp systems, allowing

234-816: A programming model designed to support generating efficient machine code, including fine-grained control over dynamic and static behaviors. It was created in the early 1990s by a group led by Apple Computer . Dylan derives from Scheme and Common Lisp and adds an integrated object system derived from the Common Lisp Object System (CLOS). In Dylan, all values (including numbers, characters, functions, and classes ) are first-class objects . Dylan supports multiple inheritance , polymorphism , multiple dispatch , keyword arguments , object introspection, pattern -based syntax extension macros , and many other advanced features. Programs can express fine-grained control over dynamism, admitting programs that occupy

273-519: A set of primitive operations on the S-expressions, and a language of meta-expressions (M-expressions) that could be used to define more complex operations. Finally, he showed how the meta-language itself could be represented with S-expressions, resulting in a system that was potentially self-hosting . The draft version of this paper is known as "AI Memo 8". McCarthy had planned to develop an automatic Lisp compiler ( LISP 2 ) using M-expressions as

312-497: A simple transformation away from S-expressions, so that theoretically they can be used on any Lisp dialect and not interfere with features like macros. Additional syntax-related include Apple's Dylan (Algol-like tokens) and Clojure 's addition of other literal syntaxes. Function notation Too Many Requests If you report this error to the Wikimedia System Administrators, please include

351-436: A single class, <view> , and contains two slots, title holding a string for the window title, and position holding an X-Y point for a corner of the window. In this example, the title has been given a default value, while the position has not. The optional init-keyword syntax allows the programmer to specify the initial value of the slot when instantiating an object of the class. In languages such as C++ or Java,

390-502: A specific class, and can be called natively by anyone. Linking a specific generic function to a method in a class is accomplished thusly: This definition is similar to those in other languages, and would likely be encapsulated within the <window> class. Note the := setter call, which is syntactic sugar for color-setter($ blue, w) . The utility of generic methods comes into its own when you consider more "generic" examples. For instance, one common function in most languages

429-470: A variety of non-alphanumeric characters as part of identifiers. Identifiers may not consist of these non-alphanumeric characters alone. If there is any ambiguity, whitespace is used. A simple class with several slots: By convention, classes are named with less-than and greater-than signs used as angle brackets , e.g. the class named <point> in the code example. In end class <point> both class and <point> are optional. This

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468-477: A whole. For example, using a String concatenation function requires importing and compiling against all of String . Some languages, including Dylan, also include a separate, explicit namespace or module system that performs encapsulation in a more general way. In Dylan, the concepts of compile-unit and import-unit are separated, and classes have nothing specifically to do with either. A library defines items that should be compiled and handled together, while

507-401: Is based on multiple dispatch (multimethods), where the specific method to be called is chosen based on the types of all its arguments. The method need not be known at compile time, the understanding being that the required function may be available, or not, based on a user's preferences. Under Java the same methods would be isolated in a specific class. To use that functionality the programmer

546-438: Is forced to import that class and refer to it explicitly to call the method. If that class is unavailable, or unknown at compile time, the application simply won't compile. In Dylan, code is isolated from storage in functions . Many classes have methods that call their own functions, thereby looking and feeling like most other OO languages. However code may also be located in generic functions , meaning they are not attached to

585-459: Is no explicit return statement . The result of a method or function is the last expression evaluated. It is a common style to leave off the semicolon after an expression in return position. In many object-oriented languages, classes are the main means of encapsulation and modularity; each class defines a namespace and controls which definitions are externally visible. Further, classes in many languages define an indivisible unit that must be used as

624-465: Is that a programmer can add functionality to existing classes by defining functions in a separate file. For instance, you might wish to add spell checking to all <string> s, which in C++ or Java would require access to the source code of the string class—and such basic classes are rarely given out in source form. In Dylan (and other "extensible languages") the spell checking method could be added in

663-429: Is the to-string , which returns some human-readable form for the object. For instance, a window might return its title and its position in parens, while a string would return itself. In Dylan these methods could all be collected into a single module called " to-string ", thereby removing this code from the definition of the class itself. If a specific object did not support a to-string , it could be easily added in

702-606: Is the I-expression , which use indentation to indicate parentheses implicitly, and are thus in some ways intermediate between S-expressions and M-expressions. I-expressions were introduced in Scheme Request For Implementation 49 as an auxiliary syntax for Scheme , but they have not been widely adopted. A further development is the "sweet" t-expression , which has infix operators without precedence. Like I-expressions, t-expressions are only

741-472: Is true for all end clauses. For example, you may write end if or just end to terminate an if statement. To make an instance of <point> : The same class, rewritten in the most minimal way possible: The slots are now both typed as <object> . The slots must be initialized manually: By convention, constant names begin with "$ ": A factorial function: Here, n! and <integer> are just normal identifiers. There

780-456: The spell-check module, defining all of the classes on which it can be applied via the define method construct. In this case the actual functionality might be defined in a single generic function, which takes a string and returns the errors. When the spell-check module is compiled into your program, all strings (and other objects) will get the added functionality. Apple Dylan is the implementation of Dylan produced by Apple Computer . It

819-414: The to-string module. This whole concept might strike some readers as very odd. The code to handle to-string for a window isn't defined in <window> ? This might not make any sense until you consider how Dylan handles the call of the to-string . In most languages when the program is compiled the to-string for <window> is looked up and replaced with a pointer (more or less) to

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858-408: The compiler to clearly understand compilable units, such as libraries . Dylan derives much of its semantics from Scheme and other Lisps; some Dylan implementations were initially built within extant Lisp systems. However, Dylan has an ALGOL -like syntax instead of a Lisp-like prefix syntax. Dylan was created in the early 1990s by a group led by Apple Computer . At one time in its development, it

897-402: The String interface, and the "concat" interface which collects together all of the different concatenation functions from various classes. This is more commonly used in math libraries, where functions tend to be applicable to widely differing object types. A more practical use of the interface construct is to build public and private versions of a module, something that other languages include as

936-408: The class would also define its interface. In this case the definition above has no explicit instructions, so in both languages access to the slots and methods is considered protected , meaning they can be used only by subclasses. To allow unrelated code to use the window instances, they must be declared public . In Dylan, these sorts of visibility rules are not considered part of the code, but of

975-528: The definition of M-expressions and uses them throughout the book to explain Lisp and its implementation. The definitions for the functions apply and eval from the Lisp 1.5 Manual, page 13. Using the function eval on an s-expression. MLisp was a contemporary (1968–1973) project to implement an M-expression-like frontend for Lisp. A few extra features like hygienic macros , pattern matching , and backtracking were incorporated. It eventually evolved into an abandoned LISP70 draft. M-LISP ( MetaLISP ) from 1989

1014-435: The definition of the storage only. For instance: In this example, the class " <window> " is defined. The <class name> syntax is convention only, to make the class names stand out—the angle brackets are merely part of the class name. In contrast, in some languages the convention is to capitalize the first letter of the class name or to prefix the name with a C or T (for example). <window> inherits from

1053-479: The design of the language and developed implementations: Harlequin released a commercial IDE for Microsoft Windows and Carnegie Mellon University released an open source compiler for Unix systems called Gwydion Dylan. Both of these implementations are now open source. The Harlequin implementation is now named Open Dylan and is maintained by a group of volunteers, the Dylan Hackers. The Dylan language

1092-408: The details below. Request from 172.68.168.150 via cp1114 cp1114, Varnish XID 918795269 Upstream caches: cp1114 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 07:47:53 GMT Dylan (programming language) Dylan is a multi-paradigm programming language that includes support for functional and object-oriented programming (OOP), and is dynamic and reflective while providing

1131-488: The dominant form of Lisp. McCarthy reflected on the fate of M-expressions in 1979: The project of defining M-expressions precisely and compiling them or at least translating them into S-expressions was neither finalized nor explicitly abandoned. It just receded into the indefinite future, and a new generation of programmers appeared who preferred internal notation to any FORTRAN-like or ALGOL-like notation that could be devised. The book Anatomy of LISP by John Allen explains

1170-478: The functionality to be included in strings, the functionality must be added to the String namespace. As soon as this occurs, the String class becomes larger, and functions that don't need to use regex still must "pay" for it in increased library size. For this reason, these sorts of add-ons are typically placed in their own namespaces and objects. The downside to this approach is that the new functions are no longer

1209-429: The language syntax and S-expressions to describe the compiler's internal processes. Stephen B. Russell read the paper and suggested to him that S-expressions were a more convenient syntax. Although McCarthy disapproved of the idea, Russell and colleague Daniel J. Edwards hand-coded an interpreter program that could execute S-expressions. This program was adopted by McCarthy's research group, establishing S-expressions as

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1248-494: The method. In Dylan this occurs when the program is first run; the runtime builds a table of method-name/parameters details and looks up methods dynamically via this table. That means that a function for a specific method can be located anywhere, not just in the compile-time unit. In the end the programmer is given considerable flexibility in terms of where to place their code, collecting it along class lines where appropriate, and functional lines where it's not. The implication here

1287-654: The module/interface system. This adds considerable flexibility. For instance, one interface used during early development could declare everything public, whereas one used in testing and deployment could limit this. With C++ or Java these changes would require changes to the source code, so people won't do it, whereas in Dylan this is a fully unrelated concept. Although this example does not use it, Dylan also supports multiple inheritance . In Dylan, methods are not intrinsically associated with any specific class; methods can be thought of as existing outside of classes. Like CLOS, Dylan

1326-515: The same time. Classes in Dylan describe slots (data members, fields, ivars, etc.) of objects in a fashion similar to most OO languages. All access to slots is via methods, as in Smalltalk . Default getter and setter methods are automatically generated based on the slot names. In contrast with most other OO languages, other methods applicable to the class are often defined outside of the class, and thus class definitions in Dylan typically include

1365-571: Was another attempt to blend M-expressions with Scheme. A parser for the " AI Memo 8" M-expression is available in Common Lisp , but the author intends it as a case against M-expressions due to its perceived inability to cope with macros. A CGOL (1977) was implemented in MacLisp and follows a similar goal of introducing Algol-like syntax with infix operators. It is known to work on Armed Bear Common Lisp . A more recent (circa 2003) variant

1404-423: Was code-named Ralph. James Joaquin chose the name Dylan for "DYnamic LANguage." Many of Dylan's syntax features come from its Lisp heritage. Originally, Dylan used a Lisp-like prefix syntax, which was based on s-expressions . By the time the language design was completed, the syntax was changed to an ALGOL-like syntax, with the expectation that it would be more familiar to a wider audience of programmers. The syntax

1443-522: Was designed by Michael Kahl. It is described in great detail in the Dylan Reference Manual. Dylan is not case sensitive . Dylan's lexical syntax allows the use of a naming convention where hyphen (minus) signs are used to connect the parts of multiple-word identifiers (sometimes called " lisp-case " or " kebab case "). This convention is common in Lisp languages. Besides alphanumeric characters and hyphen-minus signs, Dylan allows

1482-563: Was intended for use with the Apple Newton computer, but the Dylan implementation did not reach sufficient maturity in time, and Newton instead used a mix of C and the NewtonScript developed by Walter Smith. Apple ended their Dylan development effort in 1995, though they made a "technology release" version available (Apple Dylan TR1) that included an advanced integrated development environment (IDE). Two other groups contributed to

1521-756: Was manually translated from M-Expressions to S-Expressions. The in M-expressions embedded literal data, then had to be quoted in S-Expressions. The M-Expression form then needs to be transformed to the S-Expression form John McCarthy published the first paper on Lisp in 1960 while a research fellow at the Massachusetts Institute of Technology . In it he described a language of symbolic expressions ( S-expressions ) that could represent complex structures as lists. Then he defined

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