## Which parser uses first and follow?

LR based parsers also use first and follow sets, first sets are used to generate the follow sets, and follow sets are used to generate the LR table web.stanford.edu/class/archive/cs/cs143/cs143.1128/handouts/…

**Which phase of compiler do we use first and follow?**

An important part of parser table construction is to create first and follow sets. These sets can provide the actual position of any terminal in the derivation. This is done to create the parsing table where the decision of replacing T[A, t] = α with some production rule.

**How do you calculate first () follow () sets used in parsing table construction?**

Step 2: Calculate First() and Follow() for all non-terminals….

- Find First(α) and for each terminal in First(α), make entry A –> α in the table.
- If First(α) contains ε (epsilon) as terminal than, find the Follow(A) and for each terminal in Follow(A), make entry A –> α in the table.

### What are the rules to calculate first and follow?

For any production rule A → αBβ, If ∈ ∉ First(β), then Follow(B) = First(β) If ∈ ∈ First(β), then Follow(B) = { First(β) – ∈ } ∪ Follow(A)

**What is the difference between LL 1 and LR parser?**

LL Parser includes both the recursive descent parser and non-recursive descent parser….Difference between LL and LR parser.

LL Parser | LR Parser |
---|---|

It may use backtracking or dynamic programming. | It uses dynamic programming. |

LL is easier to write. | LR is difficult to write. |

Example: LL(0), LL(1) | Example: LR(0), SLR(1), LALR(1), CLR(1) |

**Why first and follow functions are used in compiler design?**

So FOLLOW can make a Non-terminal vanish out if needed to generate the string from the parse tree. The conclusions is, we need to find FIRST and FOLLOW sets for a given grammar so that the parser can properly apply the needed rule at the correct position.

## Why do we calculate first and follow?

The conclusions is, we need to find FIRST and FOLLOW sets for a given grammar so that the parser can properly apply the needed rule at the correct position.

**How do you calculate a follow set?**

An algorithm to compute the FOLLOW sets Add $ to FOLLOW(S), where S is the start nonterminal. If there is a production A → αBβ, then add every token that is in FIRST(β) to FOLLOW(B). (Do not add ε to FOLLOW(B). If there is a production A → αB, then add all members of FOLLOW(A) to FOLLOW(B).

**Why is LR better than LL?**

LL Parser includes both the recursive descent parser and non-recursive descent parser. Its one type uses backtracking while another one uses parsing table. Theses are top down parser….Difference between LL and LR parser.

LL Parser | LR Parser |
---|---|

LL is easier to write. | LR is difficult to write. |

Example: LL(0), LL(1) | Example: LR(0), SLR(1), LALR(1), CLR(1) |

### Why is LR more powerful than LL?

LR(k) is stronger than LL(k) because it provisionally matches multiple productions at the same time—each parser state encodes a set of partially-recognized productions. The parser is not required to choose between them until the right edge of the winning production.

**Which of the following is true about LR parsing?**

Which of these is true about LR parsing? Explanation: LR parsers are a type of bottom-up parsers that efficiently handle deterministic context-free languages in guaranteed linear time. 5.

**Why do we need first and follow?**

And it is able to get the string “ab” from the given grammar. So FOLLOW can make a Non-terminal vanish out if needed to generate the string from the parse tree. The conclusions is, we need to find FIRST and FOLLOW sets for a given grammar so that the parser can properly apply the needed rule at the correct position.

## How does an LL (1) parser work?

In an LL (1) parser, the parser works by maintaining a workspace initially seeded to the start symbol followed by the end-of-string marker (usually denoted $). At each step, it does one of the following:

**Is this grammar feasible for LL (1) parser?**

Here, we can see that there are two productions into the same cell. Hence, this grammar is not feasible for LL (1) Parser.

**What are the prerequisites for LL (1) parsing?**

Prerequisite — construction of LL (1) parsing table. LL (1) parsing is a top-down parsing method in the syntax analysis phase of compiler design. Required components for LL (1) parsing are input string, a stack, parsing table for given grammar, and parser.

### What does the first L in a parsing technique represent?

Here the 1st L represents that the scanning of the Input will be done from Left to Right manner and the second L shows that in this parsing technique we are going to use Left most Derivation Tree. And finally, the 1 represents the number of look-ahead, which means how many symbols are you going to see when you want to make a decision.