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Topic: Lexical variable scoping


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In the News (Thu 20 Jun 19)

  
  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.
Static scope is standard in modern functional languages such as ML and Haskell because it allows the programmer to reason as if variable bindings are carried out by substitution.
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).
en.wikipedia.org /wiki/Lexical_variable_scoping   (1125 words)

  
 VARIABLE FACTS AND INFORMATION   (Site not responding. Last check: 2007-08-18)
In computer_science and mathematics, a variable is a symbol denoting a quantity or symbolic representation.
Variables are useful in mathematics and computer_programming because they allow instructions to be specified in a general way.
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.
velocipay.com /variable   (2056 words)

  
 Static scoping
In computer science, static scoping, as opposed to dynamic scoping, is a way that the scope of free variables is determined according to its position in program code.
In lexical scoping, gimmex was defined in the scope of the outer let*, where x is 5.
C and Pascal have always had lexical scoping, which is natural since they are both influenced by the ideas that went into Algol.
www.sciencedaily.com /encyclopedia/static_scoping   (434 words)

  
 Variable   (Site not responding. Last check: 2007-08-18)
Lexical analysis of a program can determine whether variables are used out of scope.
When a variable binding extends (in time) as the program's execution passes out of the variable's scope, this is no bug.
It is a Lisp closure or a C static variable: when execution passes back into the variable's scope, the variable may be referred to again.
www.freecaviar.com /search.php?title=Variable   (1970 words)

  
 C programming language - the free encyclopedia   (Site not responding. Last check: 2007-08-18)
Today many tools are available to allow a C programmer to detect or correct various common problems, but othersare impossible to reliably detect due to the lack of constraints on C programs.
This value is highly unpredictable, and can vary between two machines, two programruns, or even two calls to the same function.
Previous C standardsdid not define a boolean type, and various (incompatible) methods were used to simulate a boolean type.
www.encyclopedia-of-knowledge.com /?t=C99   (3839 words)

  
 Namespaces   (Site not responding. Last check: 2007-08-18)
The two sets of variables are called `package variables' and `lexical variables', and they have nothing to do with each other.
If the variable wasn't declared in any block, its scope is from the place it was declared to the end of the file.
These `my variables' are sometimes called `lexical' because their scope depends only on the program text itself, and not on details of execution, such as what gets executed in what order.
perl.plover.com /FAQs/Namespaces.html   (3002 words)

  
 Static scoping : Lexical variable scoping   (Site not responding. Last check: 2007-08-18)
In computer science, static scoping, as opposed to dynamic scoping, is a way that the scope of certain variables is determined according to its position in program code.
This allows programmers to guarantee that their private variables will not accidentally be accessed or altered by functions that they call, and is considered a significant improvement over the older dynamic variable scoping.
For instance in Lisp, Emacs Lisp uses dynamic scoping (1), Common Lisp has both dynamic and lexical scoping, and Scheme uses lexical scoping exclusively.
www.termsdefined.net /le/lexical-variable-scoping.html   (499 words)

  
 Untitled Document - Variables   (Site not responding. Last check: 2007-08-18)
The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol.
Scope: Scope means where in the program a value is visible.
If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so the global binding is unchanged; this means that the change is visible in that buffer alone.
www.ugcs.caltech.edu /info/xemacs/variables_1.html   (4823 words)

  
 Star Sapphire Common LISP Reference Manual--Scope and Extent
Lexical scoping is basically a way of defining variables which take on values only while execution is occuring in a given context.
Lexical scoping is the default mechanism for establishing values for variables in Common LISP.
Lexical scope means that references to the established entity can occur only within the establishing construct.
www.webweasel.com /lisp/doc/cl03.htm   (2083 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)

  
 Online Encyclopedia and Dictionary - C programming language
This value is highly unpredictable, and can vary between two machines, two program runs, or even two calls to the same function.
Yet another common problem are variadic functions, which take a variable number of arguments.
Previous C standards did not define a boolean type, and various (incompatible) methods were used to simulate a boolean type.
www.fact-archive.com /encyclopedia/C_programming_language   (4077 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.
Lexically-scoped variables are easy to use and intuitive, in that any lexical variable refers to a variable declared within the current scope or the enclosing scope.
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 /rfc/106.html   (1471 words)

  
 Variables and Scoping (May 03)
A lexical scope provides the boundaries of some property of the program associated with the text of the program itself, as opposed to properties that are associated with the runtime state of the program.
Lexical variables do not belong to a package, so they are not able to be referenced outside the lexical scope in which they are declared.
When the subroutine returns, the lexical variables are discarded, automatically recycling the memory that had been used.
www.stonehenge.com /merlyn/UnixReview/col46.html   (1616 words)

  
 Lexical variables made default -
Perl5 provided lexical variables in a backward compatible way, along with a pragma to force either declaration of variables or import of dynamic variables.
This forced declaration of variables is generally desirable as good programming practice, although the ability does exist to turn off the pragma when necessary.
Attempts to silently make all undeclared variables lexical does not address the benefits to be gained by forcing declaration of all variables.
dev.perl.org /perl6/rfc/6.html   (601 words)

  
 Info: (elisp) Scope   (Site not responding. Last check: 2007-08-18)
(list x)) In a lexically scoped language, the binding of `x' in `binder' would never be accessible in `user', because `user' is not textually contained within the function `binder'.
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.
www.cims.nyu.edu /cgi-comment/info2html?(elisp)Scope   (235 words)

  
 3.4 Variable Access
The debugger doesn't really understand lexical scoping; it has just one namespace for all the variables in a function.
If a symbol is the name of multiple variables in the same function, then the reference appears ambiguous, even though lexical scoping specifies which value is visible at any given source location.
If the scopes of the two variables are not nested, then the debugger can resolve the ambiguity by observing that only one variable is accessible.
www.umiacs.umd.edu /~resnik/ling645_sp2002/cmu_manual/node69.html   (343 words)

  
 Variables - GeekUprising.com Forum Meta-FAQ
Lexical variables belong to no package so cannot be fully qualified with a package name.
However, when a reference to the lexical variable continues to exist outside of the code block, the lexical variable survives past the block.
Package variables are okay for short or uncomplicated Perl scripts, when you don't have to worry about intruding on the variable namespace of other routines or packages.
faq.geekuprising.com /variables   (720 words)

  
 Dynamic scoping
Dynamic variable scoping is when you scope a variable in a programming language by replacing the existing variable of that name with a new variable temporarily, for instance for the duration of a function call.
However the problem is that if one function calls another, the other may accidentally modify the first function's variables when it intended to modify a global variable instead.
Therefore over time it is becoming more common for programming languages to implement private variables with lexical variable scoping instead.
www.sciencedaily.com /encyclopedia/dynamic_scoping   (258 words)

  
 Variable Scoping   (Site not responding. Last check: 2007-08-18)
By default, all variables (and subroutines) in Perl are global
Perl also supports both lexically and dynamically scoped variables
In either case, variables disappear when the program leaves the lexical scope (ie: a block, subroutine, or file)
www.sdsc.edu /~moreland/courses/IntroPerl/slides/mt0096.htm   (45 words)

  
 Scope   (Site not responding. Last check: 2007-08-18)
The scope of a given activity or subject is the area or range of what it covers.
In computer programming, the scope of a variable refers to where and when in the program that variable can be accessed and/or modified.
It is considered good programming practice to make variables as narrow a scope as feasible so that different parts of your program do not accidentally interact with each other by modifying each other's variables.
www.city-search.org /sc/scope.html   (201 words)

  
 Info Node: (elisp)Variable Scoping   (Site not responding. Last check: 2007-08-18)
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".
Scope means where in the program a value is visible.
www.cs.vassar.edu /cgi-bin/info2www?(elisp)Variable+Scoping   (195 words)

  
 Using Explicit Ontologies in KBS Development 7   (Site not responding. Last check: 2007-08-18)
The language used for defining strategies distinguishes three types of variables: (i) instance variables (?varname), which unify with class instances, (ii) tuple variables ($varname), which unify with tuples of the indicated types and (iii) set variables (@varname) which can be used for the temporary storage of elicited instances and tuples.
Both have as their first parameter a variable, and as their second parameter an expression that constrains the instances and tuples with which the variable can unify.
The difference between elicit-all and for-each is that the former obtains the objects that are unified with the variable by asking the QUAKE user, whereas the latter searches for objects that unify with the variable in QUAKE's knowledge repository.
ksi.cpsc.ucalgary.ca /IJHCS/VH/VH7.html   (8049 words)

  
 C_language   (Site not responding. Last check: 2007-08-18)
Another reason is the desire to keep C as efficient and flexible as possible; the more powerful a language, the more difficult it is to prove things about programs written in it.
Today many tools are available to allow a C programmer to detect or correct various common problems, but others are impossible to reliably detect due to the lack of constraints on C programs.
Specifying a type in C++ is made difficult by the fact that some of the components of a declaration (such as the pointer specifier) are prefix operators while others (such as the array specifier) are postfix.
www.exoticfelines.com /search.php?title=C_language   (4211 words)

  
 C PROGRAMMING LANGUAGE FACTS AND INFORMATION   (Site not responding. Last check: 2007-08-18)
Most statements are expression statements which simply cause an expression to be evaluated -- and, in the process, cause variables to receive new values or values to be printed.
Unlike other prototyped C functions, checking the arguments of variadic functions at compile-time is not mandated by the standard, and is impossible in general without additional information.
These declaration operators are also of varying precedence, necessitating careful bracketing to achieve the desired declaration.
www.witwik.com /C_programming_language   (4868 words)

  
 LISP   (Site not responding. Last check: 2007-08-18)
A variable which refers to a given list is simply a pointer to the first cons in the list.
A major split in the modern Lisp family is between dynamic scoping and lexical scoping.
A minimalist "academic" Lisp; an early user of lexical variable scoping and continuations.
www.apawn.com /search.php?title=LISP   (4261 words)

  
 Citations: Quasi-static scoping: Sharing variable bindings across multiple lexical scopes - Lee, Friedman ...   (Site not responding. Last check: 2007-08-18)
....having two classes of variable (one treated statically and one dynamically) or one class of variable, with some other way of specifying which are rebound in any particular marshal unmarshal instance.
Their late lexical binding strategy allows the binding of lexical references and the dynamic resolution of free references.
Their proposal consists of a new abstraction called a quasi static variable that defines a mapping from a syntactic identifier to a semantic variable; identifiers in different scopes can share objects....
citeseer.lcs.mit.edu /context/504885/56290   (2001 words)

  
 Lemonodor: Hedgehog
The byte code interpreter is written in standard conforming C, is efficient and easily portable, and can be compiled to a very small executable of only some 20 kilobytes in the smallest configuration for the Intel x86 architecture.
The Hedgehog Lisp dialect has proper support for local and lambda functions, lexical scoping, variable argument functions, garbage collection, exceptions, macros, and over a hundred predefined functions or special forms.
Proper 32-bit wide integers are necessary for various bit-level operations in embedded systems.
lemonodor.com /archives/001086.html   (170 words)

  
 FlagShip FAQs
It has dynamic and lexical variable scoping, user defined commands, and functions, code blocks, nested multidimensional arrays, pre-defined object classes and other features.
Recital is a collage of all other xBase variants, plus a number of changes and additions of their own.
In the DATA segment, additional tables holding the information for dynamically scoped variables have to be maintained at runtime and are also stored in the executable.
www.fship.com /faq-fs.html   (11443 words)

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