GATE CS 2015 Set 1 — Question 18

MCQ+1 / -0.33MediumLR(0) & SLR(1)Syntax AnalysisCompiler Design

Compiler Design → Syntax Analysis → LR(0) & SLR(1)

Last updated 5 September 2026

Question

Which one of the following is TRUE at any valid state in shift-reduce parsing? (A) Viable prefixes appear only at the bottom of the stack and not inside (B) Viable prefixes appear only at the top of the stack and not inside (C) The stack contains only a set of viable prefixes (D) The stack never contains viable prefixes

Correct answer (C) The stack contains only a set of viable prefixes Solution In shift-reduce parsing, the stack contents at any point must form a viable prefix of a right sentential form. A viable prefix is a prefix of a right sentential form that can appear on the stack of a shift-reduce parser. This property ensures that as long as the stack contains a viable prefix, it is possible to continue parsing to reach the start symbol. Therefore, the stack contains only a set of viable prefixes (meaning the content of the stack is always a viable prefix). Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (C) The stack contains only a set of viable prefixes Solution In shift-reduce parsing, the stack contents at any point must form a viable prefix of a right sentential form. A viable prefix is a prefix of a right sentential form that can appear on the stack of a shift-reduce parser. This property ensures that as long as the stack contains a viable prefix, it is possible to continue parsing to reach the start symbol. Therefore, the stack contains only a set of viable prefixes (meaning the content of the stack is always a viable prefix).

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