A static scope rule is a rule for determining the static scope of a declaration. determine the type of a variable Evaluation of Dynamic Scoping: Advantage: convenience. The scope of a variable is the region of the program in which variable is declared and used. Calling Subprograms Indirectly •Usually when there are several possible subprograms to be called and the correct Static and Dynamic links in Activation Records Languages that allow nested subprograms like Pascal, Modula, Ada, and even those that don't like C, C++ and Java have run-time activation of subprograms that are managed with a stack of Activation Record Instances (ARIs). subprogram is organized as an activation record. The static scope of a declaration is that part of the program text where a use of the identifier is a reference to that particular declaration of the identifier. C, do not allow subprogram nesting. 3. Search the dynamic chain 2. A variable is visible in a statement . What is a dynamic ancestor of a subprogram? Dynamic link - to the caller of this subprogram. 17. Impossible to statically type check 3. Static scope — scope based on source pgm text (static ancestors). This concept is similar to that of accessing nonlocal variables in a static-scoped language with nested subprograms, except that the dynamic—rather than the static—chain is followed. 17. • Static scoping - Reference to x in sub2 is to big's x • Dynamic scoping - Reference to x in sub2 is to sub1's x Scope Example • Evaluation of Dynamic Scoping: - Advantage: convenience - Disadvantages: 1. The dynamic link is just the old stack top pointer; The static link must point to the most recent AR of the static parent; Two methods: Search the dynamic chain Treat subprogram calls and definitions the same as variable references and definitions b, z in sub2, y in sub1. - The static link will point to the most recent activation record of the static parent - Two methods to construct the static link: 1. Since languages t hat allow nested subprogram definitions are a generalization of those that Static Scope •Based on program text •Scope of a variable can be statically determined (prior to execution) . Define lifetime, scope, static scope, and dynamic scope. 16) Define lifetime, scope, static scope, and dynamic scope. Search the dynamic chain 2. Implementing Dynamic Scoping One way that local variables and non-local references can be implemented in a dynamic-scoped language: •Deep Access: non-local references are found by searching the activation record . What is a static ancestor of a subprogram? = The static ancestors of a subprogram sub() are all the procedures in the program within which the . Dynamic link - to the caller of this subprogram. • The scope of a variable is the range of statements over which it is visible. The dynamic chain links together all subprogram activation record instances in the reverse of the order in which they were activated. A nonlocal areference is slow if the Dynamic Scope •Based on calling sequences of program units, not their textual layout Treat subprogram calls and definitions like variable references and definitions. The lifetime begins when it is bound to a specific cell and ends when it is unbound from that cell. Define lifetime, scope, static scope, and dynamic scope. Of course, the space for the static and dynamic links and the return address will be wasted. The static link in an ARI for subprogram A points to one of the ARIs of A's static parent. A binding is dynamic if it first occurs during execution or can change during execution of the program. . 13. Therefore, the dynamic . Poor readability- it is not possible to statically. Scope — portions of pgm variable can be referenced or set. Problem Set. Answer : Residing of a subprogram under another subprogram is known as nested subprogram. Chapter 9: Subprograms 30 Overloading An overloaded subprogramis one that has the same name as another subprogram in the same referencing environment C++ and Ada have overloaded subprograms built-in, and users can write their own overloaded subprograms 2.Dynamic Scope. !Static scope rules require that the reference resolve to the most recent, compile-time binding, namely the global variable a! ♦ : 20-CS-3003: Programming Languages: Covers various significant concepts and features in the design and implementation of modern programming languages. Main calls Sub1; Sub1 calls Sub2; Sub2 calls Sub3 Answer: Variables that are visible at the last function call: 3. The lifetime begins when it is bound to a specific cell and ends when it is unbound from that cell. 17. Lifetime: A time during which the variable is bound to a specific memory location. to the static parent (where the subprogram is declared). A variable is visible in a statement if it can be referenced in that statement. It is more convenient and it provides more flexibility than static scoping. Scope is generally divided into two categories: 1.Static Scope. Summary (continued) •Static scoping provides a simple, reliable, and efficient method of allowing visibility of nonlocal variables in subprograms •Dynamic scoping provides more flexibility than static scoping but at expense of readability, reliability, and efficiency •Referencing environment of a statement is the collection of all the . nesting depth/chain offset : the difference between the static depth of the subprogram containing the reference to X and the static depth of the subprogram contining the declaration for X. Evaluation of Static Chains •Problems: 1. Find the correct activation record instance • Binding time is the time at which a binding takes place. The lifetime begins when it is bound to a specific cell and ends when it is unbound from that cell. Considering the recent declaration of x in sub1, static scoping of x in sub1 will remain in sub1 while for sub2 and sub3 static scope will be in sub1 and main respectively. What are the two steps in locating a nonlocal variable in a static-scoped language with stack-dynamic local variables and nested subprograms? 5.4.2 Type Bindings 5.4.2.1 Static Type Bindings If static, the type may be specified by either an explicit or an implicit declaration. - Local variables can be either static or stack-dynamic - Stack dynamic variables are essential to recursive . The referencing environment of a statement in a static-scoped language is the variables declared in its local scope plus the collection of all variables of its ancestor scopes that are visible. . Static scoping means that x refers to the x declared innermost scope of declaration that has one. ANSWER : The lifetime of a variable is the time during which the variable is bound to a specific memory location. None of these need to be passed in a dynamic scoped language, because they are implicitly visible in the called subprogram. The referencing environment of a statement in a static-scoped language is the variables declared in its local scope plus the collection of all variables of its ancestor scopes that are visible. Topics include various parameter passing mechanisms, dynamic and static scope rules, dynamic and static binding of subprogram names to subprogram bodies, dynamic and static data typing, eager and lazy expression evaluation, procedural and . The scope of a variable is the range of statements over which it is visible. • The r-value of a variable is its value. - Scope: The range of statements in which the variable is visible. Answer : Static Scoping • A static chain is a chain of static links that connects certain activation record instances . The scope of a variable is the range of statements over which it is visible. ~ The static link for subprogram A points to one of the ARIs of A's static parent. Since h is declared inside the global scope, the innermost x is the one in the global scope(it has no access to the xs in f and g, since it was not declared inside them), so the program prints 14 twice.. What is a dynamic ancestor of a subprogram? visibility; May be static or dynamic Binding ↑ ↓ Binding is the association of one thing with another thing ; e.g., a variable with its attributes or an operator and a symbol. The lifetime begins when it is bound to a specific cell and ends when it is unbound from that cell. What is a static ancestor of a subprogram? 13. While a subprogram is executing, its variables are visible to all subprograms it calls 2. 1. What is a static ancestor of a subprogram? Dynamic scope is a scope that is based on run-time call sequence. Treat subprogram calls and definitions like variable references and definitions Two pointers are used in activation records to enable management of the The referencing environment of a statement in a static-scoped language is the variables declared in its local scope plus the collection of all variables of its ancestor scopes that are visible. This is a property of the program text and is unrelated to the run-time call stack. The static scope of a declaration : the part of the program text where the declared identifier is used. The static chain from an ARI connects it to all of its static ancestors To find the declaration for a reference to a nonlocal variable: The compiler can easily determine how many levels of scope separate the current subprogram from the definition The static scope of a declaration. If it is determined temporally, that is dynamic scope. The scope of a variable is the range of statements over which it is visible. Define lifetime, scope, static scope, and dynamic scope. ~ A static chain is a chain of static links to connect certain ARIs. •The static linkin an activation record instance for subprogram A points to one of the activation record instances of A's static parent •The static chain from an activation record instance connects it to all of its static ancestors •Static_depthis an integer associated with a static scope whose value is the depth of nesting of that scope guaranteed to exist (or we couldn't have called the subprogram at all; that's the only time & place the function was in scope). Given the following calling sequences and assuming that dynamic scoping is used, what variables are visible during execution of the last subprogram activated? Define lifetime, scope, static scope, and dynamic scope. • A subprogram declaration provides the protocol, but not the body, of the subprogram • A formal parameter is a dummy variable listed in the subprogram header and used in the subprogram • An actual parameter represents a value or address used in the subprogram call statement Actual/Formal Parameter Correspondence • Positional a. main calls sub1; sub1 calls sub2; sub2 calls sub3.Answer: a x w in sub3. 4. 6. and i know what implementations to static scoping are there besides static chaining but it is still the most widely used, give me another reason so i can use another way for implementation. Dynamic scope: Dynamic scope refers to scope of a variable is defined at run time rather than at compile time. • The dynamic chain links all subprogram activation record instances in the reverse of the order in which they were activated. In this video, we will discuss examples of static and dynamic scoping. 14. • The subprogram call and return operations of a language are together called its subprogram linkage . Static Scoping •A static chain is a chain of static links that connects certain activation record instances •The static link in an activation record instance for subprogram A points to one of the activation record instances of A's static parent •The static chain from an activation record instance connects it to all of its static ancestors Answer : ~The static chain from ARI connects it to all of its static ancestors ~Static_depth is an integer associated with a static scope whose value is the depth of nesting of that scope. What is a dynamic ancestor of a subprogram? However, this static parent procedure . Algol 68, Pascal, Ada, JavaScript, Python, Ruby allows nesting of subprogram. A variable is visible in . It is more convenient and it provides more flexibility than static scoping. static depth : an integer associated with a static scope that indicates how deeply it is nested in the outermost scope. Static scoping also makes it much easier to make a modular code as a programmer can figure out the scope just by looking at the code. Given the following calling sequences and assuming that dynamic scoping is used, what variables are visible during execution of the last subprogram activated? Lifetime: A time during which the variable is bound to a specific memory location. Define lifetime, scope, static scope, and dynamic scope. Define lifetime, scope, static scope, and dynamic scope. 17. • A binding is an association, such as between an attribute and an entity, or between an operation and a symbol. The definition of a procedure may be directly nested within only one procedure, called its static parent procedure. Static scope is binding names to non-local variables. The dynamic scope of an association for an identifier : the set of subprogram activations in which the association is visible during execution. I understand exactly, what dynamic and static scoping is. How is a reference to a nonlocal variable in a static-scoped program con- nected to its definition? Note: This requiresthunksfor static scoping ("deep binding"). Dynamic Scope •Based on calling sequences of program units, not their textual layout As in the dynamic scoping the compiler or interpreter finds the correct instance of variable in use at its actual location so the dynamic scoping for a reference to x in . 16. • Static scope is binding names to non-local variables. = Lifetime: A time during which the variable is bound to a specific memory location. nesting depth/chain offset : the difference between the static depth of the subprogram containing the reference to X and the static depth of the subprogram contining the declaration for X. tied to the dynamic chain of subprogram activations. • In the case of dynamic scoping, the dynamic links - rather than the static links - are followed. • This method is called deep access, because access may require searches deep into the stack. Scope is the range of statements in which the variable is visible. Include with each visible variable the name of the unit where it is declared. ANSWER : The lifetime of a variable is the time during which the variable is bound to a specific memory location. dynamic chain of subprogram activations. Dynamic scope — scope based on run-time call sequence. In a statically scoped compiled language, the name of a variable is not kept in the executable program: the compiler eliminates all names in favor of addresses or base-address-offset pairs. The dynamic link is just the old stack top pointer; The static link must point to the most recent AR of the static parent; Two methods: Search the dynamic chain Treat subprogram calls and definitions the same as variable references and definitions b. + the compiler must generate code to cause implicit allocation and de-allocation of local variables at runtime + an activation record instance is dynamically created when a subprogram is called + the activation record format is fixed, but its size may be dynamic + the a declaration of a stack dynamic variable does not change the size of the . static links that connects certain activation record instances Static_depth is an integer associated with a static scope representing the scope's nesting depth The chain_offset or nesting_depth of a non-local reference is the difference between the . In this video, we will learn about the basics of scoping of variables and we will see how Static and Dynamic scoping works. Answer : The static ancestors of a subprogram sub () are all the procedures in the program within which the procedure sub () is defined, i.e., the definition of the procedure sub () is nested. Disadvantages: While a subprogram is executing, its variables are visible to all subprograms it calls. The alternative is to leave out the static and dynamic links and the return address, which saves space but makes accesses to block variables different from subprogram locals. Static depth is an interger associated with a static scope that indicated how deeply it is nested in the outermost scope. Scope - Static and Dynamic . Frame Structure: return address dynamic link static link (when using static scoping) 1-30 Static Chain Maintenance • At the call, - The activation record instance must be built - The dynamic link is just the old stack top pointer - The static link must point to the most recent ari of the static parent - Two methods: 1. Static Scoping •A static chainis a chain of static links that connects certain activation record instances •The static linkin an activation record instance for subprogram A points to one of the activation record instances of A's static parent •The static chain from an activation record instance connects it to all of its static ancestors - Bound to storage only during subprogram activation • Parameters in subprogram headers are called . Chain_offset is the length of static depth of the subprogram containing the reference to X and declaration for X. . . Answer : - Lifetime: A time during which the variable is bound to a specific memory location. Answer : b, z in sub2, y in sub1. The referencing environment of a statement in a static-scoped language is the variables declared in its local scope plus the collection of all variables of its ancestor scopes that are visible. If the "amount" of program is determined spatially, that is static (sometimes called "lexical") scope. Static Scope •Based on program text •Scope of a variable can be statically determined (prior to execution) . The referencing environment of a statement in a static-scoped language is the variables declared in its local scope plus the collection of all variables of its ancestor scopes that are visible. subprogram definitions, which create nested static scopes (e.g., Ada, . Treat subprogram calls and definitions like variable references and definitions Issues with Static Chains • Problems: 1. Example: Static versus Dynamic Scoping ! For example, in some cases, some parameters passed from one subprogram to another are variables that are defined in the caller. Static scope: Static scope is also called lexical scope. subprogram - Most natural for dynamic-scoped . A variable is visible in a statement . In most of the programming languages including C, C++ and Java, variables are always statically (or lexically) scoped i.e., binding of a variable can be determined by program text and is independent of the run-time function call stack. Static scoping is so named because the scope of a variable can be statically determined—that is, prior to execution. !Dynamic scope rules, on the other hand, require that we choose the most recent, active binding at run time »!Example use: implicit parameters to subroutines »! Answer : Static Scoping of Nested subprograms . In this video, we will discuss examples of static and dynamic scoping. • tied to the dynamic chain of subprogram activations. Static scope refers to scope of a variable is defined at compile time itself that is when the code is compiled a variable to bounded to some block. subprogram definitions, which create nested static scopes (e.g., Ada, . Given the following calling sequences and assuming that dynamic scoping is used, what variables are visible during execution of the last subprogram activated? An explicit declaration is a program statement used for declaring the types of variables. 17. What is a dynamic ancestor of a subprogram? . Static scope rules relate references Define lifetime, scope, static scope, and dynamic scope.-Lifetime — when memory is alloc'd for a variable (when in existence). 42. When a subprogram is placed within another subprogram,it gets hide from the rest of the program. Scope: The range of statements in which the variable is visible. Scope: The range of statements in which the variable is visible. a. main calls sub1; sub1 calls sub2; sub2 calls sub3.Answer: a x w in sub3. What is a static ancestor of a subprogram? What is a static ancestor of a subprogram? The dynamic link is a pointer to the base of the activation record for the enclosing scope of the activated subprogram. 13. 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