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Topic: Dynamic variable scoping


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  Scope (programming) - Wikipedia, the free encyclopedia
A namespace is a scope that uses the enclosing nature of the scope to group logically related identifiers under a single identifier.
Correct implementation of static scope in languages with first-class nested functions can be subtle, as it requires each function value to carry with it a record of the values of the variables that it depends on (the pair of the function and this environment is called a closure).
With dynamic scoping, the binding stack for the x identifier will contain two items when f is invoked: the global binding to 0, and the binding to 1 introduced in g (which is still present on the stack since the control flow hasn't left g yet).
en.wikipedia.org /wiki/Dynamic_scoping   (1125 words)

  
 VARIABLE WEALTHY AND WISE FACT FINDER   (Site not responding. Last check: 2007-11-07)
In computer_science and mathematics, a variable is a symbol denoting a quantity or symbolic representation.
Usually, a variable is set to reside in some scope in program code, and entrance and leave of the scope coincides with the beginning and ending of a variable life, respectively.
A variable may refer to a data_structure created dynamically, where many structure components are not ''directly'' named by variables, but are reachable from a variable by traversing the structure.
www.boostmoney.com /variable   (2054 words)

  
 Learn more about Scope in the online encyclopedia.   (Site not responding. Last check: 2007-11-07)
In computer programming, the scope of an identifier refers to where and when in the program the identifier can be referenced.
Scope applies to all identifiers in a program, but it is mostly used for variables, functionss and classeses.
Scope is usually hierarchical: a variable declared at local scope (for example, as a local variable inside a function) supersedes the same variable declared at global scope.
www.onlineencyclopedia.org /s/sc/scope.html   (364 words)

  
 Comm. of the ACM 21, 7 (July 1978), 565-569.
This problem is compounded by Lisp's choice of "fluid" or "dynamic" scoping for nonlocal (free) variables, wherein a procedure's free variables are considered bound in the environment of the caller (or the caller's caller, etc.).
Dynamic scoping leads to environment trees at run-time which are "tall and thin" rather than "short and bushy" because the topology of the environment tree follows that of the run-time stack rather than the block structure of the source text.
Since the length of time to access the binding of a variable in the original Lisp 1.5 implementation [6] is proportional to the distance in the tree from the current environment to the place where that variable is bound, this time can be quite large for the tall environment trees actually encountered.
home.pipeline.com /~hbaker1/ShallowBinding.html   (3316 words)

  
 No Title
An important point is that the variable is not automatically accessible in those called procedures; rather, if one of those procedures wishes to gain access back up to the dynamic variable, this desire must be explicitly indicated as well.
Thus, we might want our implementation of dynamic scoping to trace back through the chain of dynamic frames but only ``find'' a variable that matches the name in some frame if it has been explicitly declared to be an exported dynamic variable.
To reduce the risk of confusion between such lexical and dynamic variables, it is a common convention to put asterisks at the start and end of dynamic variable names.
swiss.csail.mit.edu /classes/6.001/FT98/lectures/dynamic/dynamic-notes   (1060 words)

  
 Dynamic scoping -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-11-07)
Dynamic scoping is the policy of giving values to variables that have a well-defined extent in time (during execution) instead of in space (literal distance in the source code: this is (Click link for more info and facts about lexical scoping) lexical scoping).
Generally certain (A solid piece of something (usually having flat rectangular sides)) blocks are defined to create bindings whose lifetime is the execution time of the block; this adds a hint of lexicality to the scoping.
An alternate strategy that is usually more efficient is to maintain a stack of bindings for each identifier; the stack is modified whenver the variable is bound or unbound, and a variable's value is simply that of the top binding on the stack.
www.absoluteastronomy.com /encyclopedia/d/dy/dynamic_scoping.htm   (455 words)

  
 Yet another lexical variable proposal: lexical variables made default without requiring strict 'vars' -
Undeclared variables can be considered a part of the smallest enclosing scope under the "liberal" approach to resolving the "ambiguity" mentioned in the suggestion, but they could also be considered a part of the largest enclosing scope.
Dynamic variables, on the other hand, refer to a variable from within the current scope or from within the current subroutines _caller_, which could be anywhere!
The notion of "scope" is the same as Perl has had almost since the beginning: a block (including a subroutine block) begins a new scope; a file is also a scope.
dev.perl.org /perl6/rfc/106.html   (1471 words)

  
 [No title]
You may notice that this is a little bit different from the C language in that global variables in C are automatically available to functions unless specifically overridden by a local definition.
In PHP global variables must be declared global inside a function if they are going to be used in that function.
array is an associative array with the name of the global variable being the key and the contents of that variable being the value of the array element.
www.zend.com /manual/language.variables.scope.php   (644 words)

  
 Info: (elisp) Scope   (Site not responding. Last check: 2007-11-07)
Emacs Lisp uses dynamic scoping because simple implementations of lexical scoping are slow.
In addition, every Lisp system needs to offer dynamic scoping at least as an option; if lexical scoping is the norm, there must be a way to specify dynamic scoping instead for a particular variable.
It might not be a bad thing for Emacs to offer both, but implementing it with dynamic scoping only was much easier.
www.cims.nyu.edu /cgi-comment/info2html?(elisp)Scope   (235 words)

  
 Info Node: (elisp)Variable Scoping   (Site not responding. Last check: 2007-11-07)
Scoping Rules for Variable Bindings =================================== A given symbol `foo' may have several local variable bindings, established at different places in the Lisp program, as well as a global binding.
The combination of dynamic extent and indefinite scope is called "dynamic scoping".
By contrast, most programming languages use "lexical scoping", in which references to a local variable must be located textually within the function or block that binds the variable.
www.cs.vassar.edu /cgi-bin/info2www?(elisp)Variable+Scoping   (195 words)

  
 Info: (elisp) Extent   (Site not responding. Last check: 2007-11-07)
In Emacs Lisp, a variable is valid only while the form that bound it is executing.
One alternative to dynamic extent is "indefinite extent".
This means that a variable binding can live on past the exit from the form that made the binding.
hoth.stsci.edu /cgi-bin/info2html?(elisp)Extent   (206 words)

  
 Scheme programming language - the free encyclopedia   (Site not responding. Last check: 2007-11-07)
Some see the fact that functions and variables lie in the same namespace as a disadvantage, because some functions have namesthat are common for variables.
Variables bound at the top level with a define are in global scope.
Variables bound in a let are in scope for the body of the let.
www.aaez.biz /?t=Scheme_programming_language   (1863 words)

  
 Scoping Rules   (Site not responding. Last check: 2007-11-07)
The heart of the matter is that if you look at a lisp function definition, say, and find some variables used, for which no binding is apparent in the function itself, there is no cause for worry.
It is alright as long as at the time of execution of that function the variable has a binding.
This is very different from a language like C, where a variable should have a binding in the same textual block as the usage.
www.cs.utah.edu /~karra/tutorial/html/node17.html   (267 words)

  
 GNU Emacs Lisp Reference Manual - Variable Scoping   (Site not responding. Last check: 2007-11-07)
Indefinite scope means that any part of the program can potentially access the variable binding.
Dynamic extent means that the binding lasts as long as the activation of the construct that established it.
Scope: Scope means where in the program a value is visible.
www.cs.uidaho.edu /mis/HPUX/Training/gnu_docs/elisp/elisp_127.html   (184 words)

  
 Global and 'Local' Variables   (Site not responding. Last check: 2007-11-07)
It is possible to create local variables that exist temporarily-only until a certain part of the program finishes.
The local variables are assigned values from the function invocation, and after the function returns their old values are restored.
If a variable does not exist outside the function, but is used as a function argument, once the function returns, it will remain undefined.
www.cs.utah.edu /~karra/tutorial/html/node16.html   (236 words)

  
 [No title]
=head1 CHANGES Undeclared variables can be considered a part of the smallest enclosing scope under the "liberal" approach to resolving the "ambiguity" mentioned in the suggestion, but they could also be considered a part of the largest enclosing scope.
The enclosing scope cannot see the same variable that exists within the enclosed block." Alternatively, if this RFC is adopted, but nothing is done to alert new Perl6 programmers about these possibly ambiguous cases, the programmer would receive a "Use of undefined value" warning which might suffice.
This subsection should be considered "optional." In most languages, dynamic scoping of variables offers no advantages over lexical scoping, other than dynamic assignment.
dev.perl.org /perl6/rfc/106.pod   (1541 words)

  
 C# Station - Tutorial, Links, Info - C Sharp   (Site not responding. Last check: 2007-11-07)
C# doesn't allow you to dynamically change the class of an object at runtime.
PS: I have found thread-local variable support in.NET, but it may be too slow for frequent access.
Thread-local means a global variable (with the same name) in different threads are independent, for example, the thread's ID.
www.csharp-station.com /ShowPost.aspx?PostID=6364   (616 words)

  
 Info Node: (elisp)Using Scoping   (Site not responding. Last check: 2007-11-07)
Proper Use of Dynamic Scoping ----------------------------- Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand.
Such a variable is used for communication within one program.
For example, the variable `case-fold-search' is defined as "non-`nil' means ignore case when searching"; various search and replace functions refer to it directly or through their subroutines, but do not bind or set it.
www.cs.vassar.edu /cgi-bin/info2www?(elisp)Using+Scoping   (223 words)

  
 GNU Emacs Lisp Reference Manual - Impl of Scope   (Site not responding. Last check: 2007-11-07)
We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable.
To set the variable, we search for the current binding, then store the new value into that binding.
Each variable has a standard place in which its current value is always found--the value cell of the symbol.
www.cs.uidaho.edu /mis/HPUX/Training/gnu_docs/elisp/elisp_130.html   (308 words)

  
 XEmacs Lisp Programmer's Manual - Variable Scoping   (Site not responding. Last check: 2007-11-07)
Go to the first, previous, next, last section, table of contents.
Local bindings in Emacs Lisp have indefinite scope and dynamic extent.
Scope refers to where textually in the source code the binding can be accessed.
www.iro.umontreal.ca /~fourniep/lisp/lispref_134.html   (179 words)

  
 IBM Software - IBM REXX Family - Benefits of REXX
The dynamic nature of the REXX language makes it especially suitable for interpretation.
This means that people need to learn fewer programming languages; there is no longer the need for a new command programming language for every application and operating system.
Finally, REXX has a number of unusual features, such as associative arrays and dynamic variable scoping, that make many algorithms much easier to design and implement.
www-306.ibm.com /software/awdtools/rexx/benefits.html   (710 words)

  
 ipedia.com: Scope (programming) Article   (Site not responding. Last check: 2007-11-07)
This article is about the use of the term in computer science.
In computer programming, the scope of an identifier refers to where and when in the program the identifier can...
Because of this automatic scope handling, careful management of variable, class and function names should be a requirement for any non-trivial program.
www.ipedia.com /scope__programming_.html   (335 words)

  
 Semantics of Computation Assignment #2   (Site not responding. Last check: 2007-11-07)
A lexical scanner for PROC (While with Local Variable Declarations and Procedures) is given in file
Use dynamic scoping for both variables and procedures, as this is simplest to implement.
This can be used to update states, stores, variable environments, procedure environments, and what have you.
homepages.cwi.nl /~jve/CompSem/Ass2.html   (322 words)

  
 Namespace variables   (Site not responding. Last check: 2007-11-07)
There was a wikit-page Dynamic variable scoping with a procedure dynascope.
This procedure provided access to variables in upper scope levels, with searching for the given variable in upper scope levels and upvaring it, if found.
The getFullNspcVarName procedure provides a similar support, for searching the given variable, but not in upper scope, but namespace "levels".
wiki.tcl.tk /3597   (182 words)

  
 Chapter 30 -- Writing CGI Scripts in REXX   (Site not responding. Last check: 2007-11-07)
It then explains how to read input from various sources into your REXX script, how to decode the input, how to send the document back to the client (Web browser), and how to report diagnostics and errors.
is the name of the environment variable whose setting is to be returned.
If errors are encountered (for example, no input is provided, invalid characters are found, too many arguments are specified, you requested an invalid command to be executed, or an invalid syntax appears in the REXX script), the script should provide detailed information on what is wrong.
docs.rinet.ru:8083 /CGI3.2/ch30.htm   (3294 words)

  
 scoping - OneLook Dictionary Search
We found 6 dictionaries with English definitions that include the word scoping:
Tip: Click on the first link on a line below to go directly to a page where "scoping" is defined.
Phrases that include scoping: lexical scoping, dynamic scoping, dynamic variable scoping, kidney scoping, lexical variable scoping, more...
www.onelook.com /?w=scoping&ls=a   (147 words)

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