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Computer Programming Articles
Page 9 of 18
Consider the ambiguous grammar.nE → E + EnE → E * EnE → (E)nE → idn(a) Construct LR (0) items for above grammar.n(b) Construct SLR parsing table for grammar.n(c) Parse the input string id + id * id.
Problem Statement Consider the ambiguous grammar.E → E + EE → E * EE → (E)E → id(a) Construct LR (0) items for above grammar.(b) Construct SLR parsing table for grammar.(c) Parse the input string id + id * id. 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, ...
Read MoreWhat is Shift Reduce Parser?
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 MoreShow that the following grammar is LR (1)nS → A a |b A c |B c | b B anA → dnB → d
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 MoreConsider the GrammarnS → CCnC → c C | dnConstruct the parsing table for LALR (1) parser.
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 MoreWhat is LALR (1) Parser?
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 MoreFind Canonical Parsing Table (CLR) or LR (1) Parsing Table for Grammar.nS → CCnC → c C | d
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 MoreWhat is CLR (1) Parser?
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 MoreConstruct the SLR Parsing table for the following grammar. Also, Parse the input string a * b + a.
Description − Consider the GrammarE → E + T|TT → TF|FF → F*|a|b.SolutionStep1 − Construct the augmented grammar and number the productions.(0) E′ → E(1) E → E + T(2) E → T(3) T → TF(4) T → F(5) F → F ∗(6) F → a(7) F → b.Step2 − Find closure & goto Functions to construct LR (0) items.Box represents the New states, and the circle represents the Repeating State.Computation of FOLLOWWe can find outFOLLOW(E) = {+, $}FOLLOW(T) = {+, a, b, $}FOLLOW(F) = {+, *, a, b, $}Parsing for Input String a * b + a −Stack ...
Read MoreConstruct SLR (1) parsing table for the following grammarnS → x A y |x B y |x A znA → q s | qnB → q
SolutionStep1 − Construct Augmented Grammar(0) S′ → S(1) S → x A y(2) S → x B y(3) A → q S(4) A → q(5) B → qStep2 − Find Closure & goto functions to construct LR (0) items. Here Boxes represent New States and Circles represent the repeating state.Step3 − Computation of FOLLOWS → x A yFOLLOW(S) = {$} (1)Applying Rules (2a) of FOLLOW.Comparing S → x a y with A → ...
Read MoreShow that every SLR (1) is unambiguous, but some unambiguous grammars are not SLR (1). Check this for the following productions.nS → L = RnS → RnL →* RnL → idnR → L
SolutionStep1 − First of all, convert it into augmented grammar G′ and number the productions(0) S′ → S(1) S → L = R(2) S → R(3) L →∗ R(4) L → id(5) R → LStep2 − Find closure and goto function to construct LR (0) items.In the following set of LR (0) items, Boxes represents the new states and circle represents Repeating statesStep3− Computation of FOLLOW− Applying Rule (1) of FOLLOW, we getFOLLOW(S) = $ (1)S ...
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