Introduction-to-SLR-LR-parseParsing.pptx

Shift-Reduce Parsing (SLR Parsing) is a type of LR Parsing that is used to examine the syntax of a given input string. Head over to the below blog to get a better understanding of SLR Parser. The article thoroughly covers the key elements of the Shift-Reduce Parsing (SLR Parsing) algorithm.

1. NADAR SARASWATHI COLLEGE OF ARTS AND SCIENCE By P.JEYA SHRI NITHI I M.Sc(CS)

2. I n t r o d u c t i o n t o S L R Parsing SLR parsing is a bottom-up parsing technique used in compiler construction to analyze the syntax of a programming language. It is a popular choice due to its simplicity and efficiency. J P

3. C o n t e x t -F r ee G r afifia r s Context-free grammars (CFGs) are used to define the syntax of a programming language. They specify the rules for constructing valid sentences in the language. A CFG consists of a set of non-terminal symbols, terminal symbols, a start symbol, and a set of production rules. 1 Non - t e r fiinal S y fibols Represent grammatical categories or phrases, such as "expression" or "statement." 2 T e r fiinal S y fibols Represent the actual symbols that appear in the input string, such as keywords, identifiers, and operators. 3 P r odu c tion R ules Describe how to derive a string of terminal symbols from the start symbol. fi S t a r t S y fibol Represents the root of the parse tree and the starting point for deriving sentences.

4. Fini t e A u t ofia t a and P a r sing Finite automata are mathematical models that describe a sequence of states and transitions. They play a crucial role in parsing by recognizing valid sequences of input symbols. 1 Input St r ing The string of input tokens is processed one symbol at a time. 2 S t a t e T r ansitions The automaton transitions between states based on the current input symbol. 3 Acceptance If the automaton reaches a final state after processing the entire input string, the input is recognized as valid.

5. C onst r u c ting SLR P a r sing T ables SLR parsing tables are constructed using the information obtained from the CFG and the corresponding finite automaton. The table guides the parser through the process of recognizing and constructing a parse tree for the input string. State Input Symbol Action id Shift 1 1 + Reduc e b y A -> id 2 $ Accept

6. C anoni c al LR(1) P a r sing Canonical LR(1) parsing is a more powerful and general parsing technique compared to SLR. It uses a larger set of states and transitions in the finite automaton, leading to more accurate and robust parsing. SLR P a r sing Uses a single state for each non-terminal symbol. Simpler to implement but less powerful. C anoni c al LR(1) P a r sing Uses multiple states for each non-terminal symbol. More powerful but complex to implement.

7. Di f f e r en c es b e t w een SLR and C anoni c al LR SLR and Canonical LR parsing differ in the way they handle conflicts during parsing. SLR uses a simpler approach, which can lead to conflicts that need to be resolved manually. Canonical LR, on the other hand, resolves these conflicts automatically by utilizing a more comprehensive set of states. SLR Simpler to implement. C anoni c al LR Handles more complex grammars. SLR Can lead to parsing conflicts. C anoni c al LR More complex to implement.

8. A d v a n t ages and Lifii t ations o f SLR P a r sing SLR parsing offers advantages in terms of simplicity and efficiency, making it suitable for parsing grammars with relatively simple structures. However, it has limitations when handling complex grammars with ambiguities or conflicts. 1 Advantages Easy to implement. 2 Lifiitations Not suitable for all grammars. 3 Applications Used in various compilers and interpreters.

9. P r ac ti c al C onside r ations and Applications SLR parsing finds applications in various compiler construction scenarios. It is particularly well-suited for parsing languages with simpler syntax and fewer ambiguities. The choice between SLR and Canonical LR depends on the specific requirements of the compiler. C ofipiler Design SLR parsing is used to analyze and translate source code into machine code. L anguage P r o c essing It is utilized in tools for natural language processing, such as parsers and grammars. F o r fial V e r ifi cation SLR parsing is used to check the correctness and consistency of formal specifications.

10. Introduction to Canonical LR Parsing Canonical LR parsing is a powerful bottom-up parsing technique widely used in compiler design. It's known for its efficiency and ability to handle a wide range of programming language constructs. This presentation aims to explore the fundamentals of canonical LR parsing, delving into its principles, construction, and implementation. JP

11. LR Parsing Automata LR parsing automata are finite-state machines that efficiently recognize valid input strings based on the grammar rules. They operate on a stack, reading the input one symbol at a time and maintaining a state to track the parsing progress. 1 State Represents the parsing context and the current position in the grammar. 2 Stack Stores the symbols that have been successfully parsed, providing the current parsing context. 3 Input Buffer Contains the remaining input symbols to be parsed. 4 Action Table Specifies the parsing action (shift, reduce, or accept) for each state and input symbol. 5 Goto Table Indicates the next state to transition to based on the current state and the input symbol.

12. Constructing the LR(0) Automaton The LR(0) automaton is the foundation for canonical LR parsing. It's constructed through a systematic process of exploring all possible parsing states and their transitions based on the grammar. Start Symbol The initial state is determined by the start symbol of the grammar. Closure Operation Expands the states by including all possible production rule right-hand sides (RHS) that can be derived from the left-hand side (LHS) of the current state. Goto Function Computes transitions between states based on the input symbol.

13. Canonical LR(1) Parsing Tables The LR(1) parsing tables are constructed from the LR(0) automaton by incorporating lookahead symbols. The tables specify the parsing action (shift, reduce, or accept) and the next state for each state and input symbol. State Input Symbol Action a shift, 1 1 b shift, 2 2 $ reduce, 1

14. Handling Shift-Reduce and Reduce-Reduce Conflicts Conflicts arise when multiple parsing actions are possible for a given state and input symbol. Shift-reduce conflicts occur when both a shift and a reduce action are valid, while reduce-reduce conflicts arise when multiple reduce actions are possible. Shift-Reduce Conflicts Occur when the parser can either shift the current input symbol or reduce the top of the stack. Reduce-Reduce Conflicts Occur when the parser can reduce the top of the stack using multiple production rules. Conflict Resolution The choice between conflicting actions can be resolved by using various techniques, such as precedence rules, associativity rules, or operator-precedence grammars.

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