Found 213 Articles for Computer Programming

There are three types of LR Parsers which are as follows −Simple LR Parser (SLR) − SLR represents "Simple LR Parser". It is very easy and costeffective to execute. But it fails to make a parsing table for some class of grammars, i.e., why CLR and LALR are used which implements mainly all class or type of grammars. It constructs parsing tables which helps to perform parsing of input strings. SLR Parsing can be done if context-free Grammar will be given. In LR (0), 0 means there is no Look Ahead symbol.The SLR parsing action and goto function from the ... Read More

LR Parser is a class of Bottom-Up Parser that is used to parse Context-Free Grammars. LR Parsing is known as LR (K) parsing. LR parser is a shift-reduce parser that creates the use of deterministic finite automata, identifying the collection of all applicable prefixes by reading the stack from bottom to top.It decides what handle, if any, is available. A viable prefix of a right sequential form is that prefix that includes a handle, but no symbol to the right of the handle. Thus, if a finite state machine that identifies viable prefixes of the right sentential form is constructed, ... Read More

LR Parsing Tables are a two-dimensional array in which each entry represents an Action or goto entry. A programming language grammar having a large number of productions has a large number of states or items, i.e., I0, I1 … … In.So, due to more states, more Actions & goto entries will be filled, which requires a lot of memory. So, a two-dimensional array is not sufficient to store so many action entries, because each entry requires at least 8 bits to encode.So, we have to use more efficient encoding than a two-dimensional array for encoding, Action & goto field.For example, ... Read More

SolutionStep1− Construct Augmented Grammar(0) E′ → S(1) E → E + E(2) E → E ∗ E(3) E → (E)(4) E → idStep2− Find closure & goto functions to construct LR (0) items.Closure (E′ → ∙ E) =Applying goto on I9∵ goto cannot be applied on I9, as the dot in E → (E). is on the last position.Step3− Computation of FOLLOWApplying Rule (1) FOLLOWFOLLOW(B) = {$}                                                         (1)E → E + EComparing ... Read More

Shift Reduce Parser is a type of Bottom-Up Parser. It generates the Parse Tree from Leaves to the Root. In Shift Reduce Parser, the input string will be reduced to the starting symbol. This reduction can be produced by handling the rightmost derivation in reverse, i.e., from starting symbol to the input string.Shift Reduce Parser requires two Data StructuresInput BufferStackThere are the various steps of Shift Reduce Parsing which are as follows −There are the various steps of Shift Reduce Parsing which are as follows −It uses a stack and an input buffer.Insert $ at the bottom of the stack ... Read More

SolutionStep1 − Construct Augment Grammar(0) S′ → S(1) S → A a(2) S → b A c(3) S → B c(4) S → b B a(5) A → d(6) B → dStep2 − Find Closure & goto. Construct a set of LR (1) items. Here all the boxes represent new states.LR (1) Parsing TableSo, the LR (1) Parsing Table has no several entries. Grammar is LR (1).Construction of LR (1) or Canonical LR Parsing TableInput − An Augmented Grammar G’.Output − The Canonical LR (1) Parsing TableMethodFilling the "shift" Entries(s) − Apply Rule (2a) of construction of CLR Parsing Table.Consider ... Read More

SolutionStep1 − Construct LR (1) Set of items. First of all, all the LR (1) set of items should be generated.In these states, states I3 and I6 can be merged because they have the same core or first component but a different second component of Look Ahead.Similarly, states I4 and I7 are the same.Similarly, states I8 and I9 are the same.So, I3 and I6 can be combined to make I36.I4 and I7 combined to make I47.I8 and I9 combined to make I89.So, the states will be∴ I3 = goto (I0, c)But I3 , I6 combined to make I36∴ I36 = ... Read More

LALR Parser is Look Ahead LR Parser. It is intermediate in power between SLR and CLR parser. It is the compaction of CLR Parser, and hence tables obtained in this will be smaller than CLR Parsing Table.Here, first of all, we will construct LR (1) items. Next, we will look for the items having the same first component, and they are merged to form a single set of items. It means the states have the same first component, but the different second component can be integrated into a single state or item.For Example.Suppose ifI4: C → d ∙ , c ... Read More

SolutionStep1 − Construct Augmented Grammar(0) S′ → S(1) S → CC(2) C → cC(3) C → d.Step2 − Find closure & goto to construct LR (1) itemsApplying goto on I7, I8, I9In I7, I8, I9 we have production C → d ∙, $, c → cC ∙, c | d and ∙ C → cC ∙, $ respectively, i.e., the dot cannot be shifted further.So, goto cannot be applied to I7, I8, I9.Drawing DFAFirst of all, 10 states, i.e., I0 to I9 will act as nodes for DFA.Edges are joined using goto statements. For example, goto(I0, S) = I1∴ There ... Read More

CLR defines canonical lookahead. CLR parsing use the canonical collection of LR (1) items to construct the CLR (1) parsing table. CLR (1) parsing table makes the more number of states as compare to the SLR (1) parsing. In the CLR (1), it can locate the reduce node only in the lookahead symbols.Working of CLR ParserConstruction of LR (1) collection of items for GrammarIt requires three thingsAugmented GrammarClosure Functiongoto FunctionAugmented Grammar  It is a new Grammar G′ which contains a new productionS′ → S with all other productions of given grammar G.Closureprocedure closure (I)begin Repeat for each item A → ... Read More