Symbol Table is a data structure that supports an effective and efficient way of storing information about various names appearing in the source program. These names are used in the source code to identify the different program elements, like a variable, constants, procedures, and the labels of statements.The symbol table is searched each time a name is encountered in the source text. When a new name or new data about an existing name is found, the content of the symbol table modifies.Therefore, the symbol table must have an efficient mechanism for accessing the data held in the table also for ... Read More

SolutionThe first number the production as below −Step1− Construct Augmented Grammar(0) S′ → S(1) S → A a(2) S → b A c(3) S → d c(4) S → b d a(5) A → dStep2− Find Closure & goto. Find the canonical set of LR (1) items for the Grammar.In the states, I0 to I10, no states have a similar first element or core. So, we cannot merge the states. Some states will be taken for building the LALR parsing table.LALR Parsing TableParsing of String "bdc"StackInput StringAction$ 0bdc $Shift 3$ 0 b 3dc $Shift 7$ 0 b 3 d 7c ... Read More

Problem Statement Verifying whether the string id * id + id is accepted by a given grammar using SLR parsingConsider the SLR parsing table for the GrammarE → E + TE → TT → T ∗ FT → FF → (E)F → idCheck whether the string id * id + id is accepted or not by using the SLR parsing table constructed in the example. SolutionInitially, LR Parser in state 0.Put $ at the end of the string, i.e., id * id + id $.StackInput StringReason0id ∗ ... Read More

Deterministic Finite Automata (DFA)Deterministic means that on each input there is one and only one state to which the automata can have the transition from its current state. In deterministic finite automata, the head can move only in one direction to scan the input tape symbols. But in the case of two-way, finite automata on scanning an input symbol the head of the tape may move in right or left from its current position.There are two ways to represent Deterministic finite Automata −Transition DiagramIt is a directed graph or flow chart having states and edges. A strong path through a ... Read More

An Activation Record is a data structure that is activated/ created when a procedure/function is invoked, and it includes the following data about the function.Activation Record in 'C' language consist ofActual ParametersNumber of ArgumentsReturn AddressReturn ValueOld Stack Pointer (SP)Local Data in a function or procedureHere, Old SP stores the value of stack pointer of Activation Record of procedure which has called this procedure which leads to the generation of this Activation Record, i.e., It is a pointer to the activation record of the caller.In Stack Allocation Scheme, when procedure A calls Procedure B, the activation record for B will be ... Read More

There are various storage allocation techniques are as follows −Static AllocationIt is the simplest allocation scheme in which allocation of data objects is done at compile time because the size of every data item can be determined by the compiler.Recursive Subprogram and Arrays of adjustable length are not permitted in a language. In static allocation, the compiler can decide the amount of storage needed by each data object. Thus, it becomes easy for a compiler to identify the address of these data in the activation record.FORTRAN uses this kind of storage allocation strategies.AdvantagesIt is easy to implement.It allows type checking ... Read More

ListsIt is conceptually simplest and easy to implement a data structure for the symbol table in a linear list of records, as shown below −It can use an individual array to store the name and its associated information. New Names are inserted to the list in the order in which they are encountered. It can retrieve data about a name we search from the starting of the array up to the position marked by the pointer AVAILABLE which indicates the beginning of the empty portion of the array.When the name is placed, the associated data can be discovered in the ... Read More

An access link is a pointer to each activation record that obtains a direct implementation of lexical scope for nested procedures. In other words, an access link is used to implement lexically scoped language. An “access line” can be required to place data required by the called procedure.An improved scheme for handling static links defined at various lexical levels is the usage of a data structure called display. A display is an array of pointers to the activation records. Display [0] contains a pointer to the activation record of the most recent activation of a procedure defined at lexical level ... Read More

Search TreeA more effective technique to symbol table organization is to add two link fields, LEFT and RIGHT, to every record. We use these fields to link the records into a binary search tree.This tree has the property that all names NAME (j) accessible from NAME (i) by following the link LEFT (i) and then following any sequence of links will precede NAME (i) in alphabetical order (symbolically, NAME (j) < NAME (i))Similarly, all names NAME (k) accessible starting with RIGHT (i) will have the property that NAME (i) < NAME (k). Thus, if we are searching for NAME and ... Read More

Representing scope information is a concept in which the scope of each variable name is preserved in the symbol table so that we can use the same name in different blocks and different locations. Representing name in symbol table along with an indicator of the block in which it appears.Suppose we have a variable name 'a' in block A and the same variable in block B. Suppose it can store 'a' in the symbol table without block information. In that case, it will only keep the first instance of 'a' which it encounters, hence to overcome this problem names are ... Read More