Introduction-to-LR-Parsers-&-Canonical-Collections-of-LR(0)-items.pptx
- 1. NADAR SARASWATHI COLLEGE OF ARTS AND SCIENCE DEPARTMENT OF COMPUTER SCIENCE LR PARSERS & THE CANONICAL COLLECTIONS OF LR(0) ITEMS BY: D.Aki Akshaya
- 2. Introduction to LR Parsers LR parsers are a powerful tool for analyzing and understanding context-free grammars. They are widely used in compilers and interpreters for parsing programming languages. They scan the input from left to right and produce a rightmost derivation in reverse. Types of LR parsers include SLR, LALR, and Canonical LR, each offering different levels of parsing power and complexity.
- 3. Definition of LR(0) Items LR(0) items are a crucial element in LR parsing. They represent the current state of the parser, signifying the location of the dot within a production rule. They can be classified as either "kernel" items, representing the initial state, or "non-kernel" items, derived from other items. LR(0) items are a key element in LR parsing. They represent a state of a parser, marking the position of the parser's dot within a production rule.
- 4. Construction of the LR(0) Item Set The LR(0) item set is built iteratively, starting with an initial item set containing the initial state. New items are added based on the grammar and the rules. 1 Initial Item Set It contains the initial state and any items derivable from it. 2 Closure Operation This step ensures that all items reachable from the current set are included. 3 Goto Function This function defines transitions between item sets, based on input symbols. 4 Iteration The process continues until all items have been included and all transitions are defined.
- 5. Closure Operation in LR(0) Item Sets The closure operation ensures that all items reachable from a given set are included, guaranteeing a complete and consistent LR(0) item set. Purpose To include all reachable items, ensuring a complete and consistent LR(0) item set. Process It involves repeatedly adding items that can be derived from existing items in the set. Result A closed item set, containing all reachable items, guaranteeing a complete parsing state.
- 6. Goto Function in LR(0) Item Sets The goto function defines transitions between LR(0) item sets, enabling the parser to move between states based on the input symbols. Purpose To define transitions between item sets, guiding the parser between states based on input symbols Process It maps a state and an input symbol to another state, representing the transition. Result A set of transitions defining the movement of the parser.
- 7. Canonical Collections of LR(0) Items The canonical collection of LR(0) items is a set of all possible LR(0) item sets for a given grammar, providing a complete representation of the parsing states. Definition A collection of all possible LR(0) item sets for a given grammar. Purpose To provide a complete representation of the parsing states, allowing for unambiguous parsing. Construction It's built iteratively by applying closure and goto operations to derive all possible item sets.
- 8. Building the LR(0) Item Set Collection The LR(0) item set collection is built by iteratively applying closure and goto functions to the initial item set, ensuring that all possible states are captured. Initial Item Set Begin with the initial item set containing the start symbol. Closure Operation Apply closure to generate all reachable items from the initial set. Goto Function Use the goto function to create new item sets for each input symbol. Iteration Repeat the closure and goto steps until no new item sets can be created.
- 9. Conflict Resolution in LR(0) Item Sets Conflicts can arise in LR(0) item sets when multiple actions are possible for the same input symbol, leading to ambiguity in parsing. Shift-Reduce Conflicts Occur when the parser can choose to either shift an input symbol onto the stack or reduce a production rule. Reduce-Reduce Conflicts Occur when the parser can choose to reduce multiple production rules, resulting in ambiguity. Resolution Techniques Methods like LALR(1) and SLR(1) parsing are used to resolve conflicts by adding lookahead symbols.
- 10. Applications of LR Parsers LR parsers are widely used in various applications, including compilers, interpreters, and programming language tools. Compilers and Interpreters They are used for parsing programming languages, ensuring correct syntax and structure. Syntax Tree Generation They are used to construct abstract syntax trees from source code, representing the structure of the program. Code Editors and IDEs They provide syntax highlighting, error detection, and other code analysis features.
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