Table of Contents

## What is left recursive and right recursive?

With right recursion, no reduction takes place until the entire list of elements has been read; with left recursion, a reduction takes place as each new list element is encountered.

**What is meant by left recursion?**

In the formal language theory of computer science, left recursion is a special case of recursion where a string is recognized as part of a language by the fact that it decomposes into a string from that same language (on the left) and a suffix (on the right).

**Why do we need to convert a left recursive grammar to its equivalent right recursive form?**

Left recursive grammar is not suitable for Top down parsers. This is because it makes the parser enter into an infinite loop. To avoid this situation, it is converted into its equivalent right recursive grammar. This is done by eliminating left recursion from the left recursive grammar.

### What is right recursion?

A recursive grammar is said to be right recursive if the rightmost variable of RHS is same as variable of LHS.

**What is LR grammar?**

LR Parser is a class of Bottom-Up Parser that is used to parse Context-Free Grammars. LR Parsing is known as LR (K) parsing where. L represents Left to Right Scanning of Input. R represents Rightmost Derivation. K is the number of input symbols of Look ahead that are used in developing parsing decisions.

**What is left recursion in ATC?**

1. Left Recursion- A production of grammar is said to have left recursion if the leftmost variable of its RHS is same as variable of its LHS.

#### What do you understand by left recursion and left factoring?

Left recursion: when one or more productions can be reached from themselves with no tokens consumed in-between. Left factoring: a process of transformation, turning the grammar from a left-recursive form to an equivalent non-left-recursive form.

**What do you mean by left recursion and left factoring in the grammar explain with the help of example?**

**Can a grammar be left and right recursive?**

A production can be recursive without being either left- or right-recursive, and it can even be both left- and right-recursive. The above examples are both direct recursion; the non-terminal directly derives a sequence containing the non-terminal. Recursion can also be indirect; it is still recursion.

## Why We Use left factoring?

Left factoring transforms the grammar to make it useful for top-down parsers. In this technique, we make one production for each common prefixes and the rest of the derivation is added by new productions.

**What is the difference between lr0 and lr1?**

Difference between LR(0) and LR(1) algorithm LR(0)requires just the canonical items for the construction of a parsing table, but LR(1) requires the loookahead symbol as well. LR(1) allows us to choose the correct reductions and allows the use of grammar that are not uniquely invertible while LR(0) does not.

**What is the difference between left factoring and left recursion?**

Left Factoring is a grammar transformation technique. It consists in “factoring out” prefixes which are common to two or more productions. Left Recursion is a property a grammar has whenever you can derive from a given variable (non terminal) a rhs that begins with the same variable, in one or more steps.

### What is indirect left recursion?

Indirect Left Recursion: A grammar is said to have indirect left recursion if, starting from any symbol of the grammar, it is possible to derive a string whose head is that symbol. For example, A –> Br B –> Cd C –> At. Where A, B, C are non-terminals and r, d, t are terminals.

**What is left recursion differentiate between immediate left recursion and indirect left recursion?**

A grammar is called immediately left recursive if it possesses an immediately left recursive production. INDIRECT LEFT RECURSION. A grammar is said to posess indirect left recursion if it is possible, starting from any symbol of the grammar, to derive a string whose head is that symbol.

**What is the purpose of left factoring?**

Left factoring is a grammar transformation that is useful for producing grammar suitable for predictive or top-down parsing.

#### What is the difference between left recursion and left factoring?

**Why do we use left recursion?**

“Any kind of sequence can be defined using either left recursion or right recursion, but you should always use left recursion, because it can parse a sequence of any number of elements with bounded stack space.

**Is there a difference between right recursion and left recursion?**

No, they all have different meanings. Right- and left-recursion refer to recursion within production rules.

## How do you get rid of left recursion?

Left Recursion can be eliminated by introducing new non-terminal A such that. This type of recursion is also called Immediate Left Recursion. In Left Recursive Grammar, expansion of A will generate Aα, Aαα, Aααα at each step, causing it to enter into an infinite loop

**Can a production be recursive without being left-or right-recursive?**

A production can be recursive without being either left- or right-recursive, and it can even be both left- and right-recursive. The above examples are both direct recursion; the non-terminal directly derives a sequence containing the non-terminal. Recursion can also be indirect; it is still recursion.

**How do you know if grammar is recursive?**

A Grammar G (V, T, P, S) is left recursive if it has a production in the form. A → A α |β. The above Grammar is left recursive because the left of production is occurring at a first position on the right side of production.