Understanding LR(0) Parser: Constructing Parsing Tables

[22990atinesh]

I've read SLR(1), LR(1) and LALR(1) parser. But what is LR(0) Parser, how can we construct parsing table for LR(0) parser.

 

[jedishrfu]

Is this a homework problem?

If so we need it posted with the homework template so we know your level of understanding, the problem statement, what you think is relevant and what you've tried.

 

[22990atinesh]

Is this a homework problem?

If so we need it posted with the homework template so we know your level of understanding, the problem statement, what you think is relevant and what you've tried.

This is not a home work question. I'd this little confusion from past few months.

 

[jedishrfu]

Theres a Wikipedia article on LR parsers that may help.

http://en.m.wikipedia.org/wiki/LR_parser#Constructing_LR.280.29_parsing_tables

 

[LudusRex]

LR(0) parser is a type of shift-reduce parser that uses a bottom-up approach to construct a parsing table for a given grammar. It is a simpler version of LR(1) parser, in which it does not take into account the lookahead symbols while constructing the parsing table. This makes LR(0) parser less powerful but also more efficient in terms of time and space complexity.

To construct a parsing table for LR(0) parser, we follow these steps:

1. Augment the grammar: Add a new start symbol S' and a new production rule S' -> S, where S is the original start symbol.

2. Compute the closure of the initial state: The initial state of the LR(0) parser is the closure of the item [S' -> .S]. The closure of an item is the set of all items that can be derived from it using the production rules of the grammar.

3. Compute the transition function: For each item in the closure, we compute the transition function for each terminal and non-terminal symbol. The transition function tells us which state to go to when we see a particular symbol.

4. Generate the parsing table: The parsing table is a matrix that contains the actions to be taken for each state and input symbol. The actions can be either shift (move to the next state) or reduce (apply a production rule). If there is a conflict, we use the precedence rules to determine the action.

5. Repeat steps 2-4 for all the states until we have constructed the complete parsing table.

In summary, LR(0) parser is a simpler version of LR(1) parser that constructs a parsing table without considering the lookahead symbols. This makes it more efficient but also less powerful. By following the steps outlined above, we can construct a parsing table for a given grammar using LR(0) parser.