A **context**-**free grammar** is a set of recursive rules used to generate patterns of strings. A **context**-**free grammar** can describe all regular languages and more, but they cannot describe all possible languages. **Context**-**free grammars** are studied in fields of theoretical computer science, **compiler design**, and linguistics.

**What is context in grammar?** A context-sensitive grammar (CSG) is a formal grammar in which the left-hand sides and right-hand sides of any production rules may be surrounded by a context of terminal and nonterminal symbols. Context-sensitive grammars are less general (in the same sense) than unrestricted grammars.

## what is context free grammar with example?

A context-free grammar (CFG) consists of a set of productions that you use to replace a vari- able by a string of variables and terminals. The language of a grammar is the set of**strings**it generates. A language is context-free if there is a CFG for it.

**What is the difference between CFG and regular grammar?** Regular grammar is either right or left linear, whereas context free grammar is basically any combination of terminals and non-terminals. Since regular grammars are non-ambiguous, there is only one production rule for a given non-terminal, whereas there can be more than one in the case of a context-free grammar.

## what are the uses of context free grammar?

**Context**-**free grammars** are **used** in compilers and in particular for parsing, taking a string-based program and figuring out what it means. Typically, CFGs are **used** to define the high-level structure of a programming language. Figuring out how a particular string was derived tells us about its structure and meaning.

**What are the components of context free grammar?** A context free grammar has 4 components: – A set of tokens, known as terminal symbols. – A set of nonterminals. nonterminal, called the left side of the production, an arrow, and a sequence of tokens and/or nonterminals, called the right side of the production.

## what is grammar in compiler design?

**Grammars** are used to describe the syntax of a programming language. It specifies the structure of expression and statements. stmt -> if (expr) then stmt.

**How do you derive leftmost?** Leftmost derivation − A leftmost derivation is obtained by applying production to the leftmost variable in each step. Rightmost derivation − A rightmost derivation is obtained by applying production to the rightmost variable in each step.

### What is CFG example?

In **CFG**, the start symbol is used to derive the string. You can derive the string by repeatedly replacing a non-terminal by the right hand side of the production, until all non-terminal have been replaced by terminal symbols. **Example**: L= {wcw^{R} | w € (a, b)*}

**Which type of grammar is more powerful and why?** As Tim said, unrestricted grammars are more powerful. In fact, they can generate the whole class of recursively enumerable (R.E.) languages, i.e., those that are accepted by Turing machines.

### How do you fix ambiguous grammar?

2 Answers Ambiguous: E → E + E | E ∗ E | (E) | a. Unambiguous: E → E + T | T T → T ∗ F | F F → (E) | a. Without the external information, there is no way to make the transformation. With the external information, we can tell that: a * a + b * b. Comment. ε is the empty string. ε is not the empty string. Associativity.

### How do you show grammar is unambiguous?

In particular, in order to prove that a grammar G = (V,T,P,S) is unambiguous, it is necessary to prove that there is only one leftmost derivation (or rightmost derivation, or parse tree) of any given string w ∈ T∗ from the start variable S.

### What is ll1 grammar?

LL(1) grammar is Context free unambiguous grammar which can be parsed by LL(1) parsers. In LL(1) First L stands for scanning input from Left to Right. Second L stands for Left Most Derivation. 1 stands for using one input symbol at each step.

### What is ambiguous grammar explain with example?

Ambiguous grammar. In computer science, an ambiguous grammar is a context-free grammar for which there exists a string that can have more than one leftmost derivation or parse tree, while an unambiguous grammar is a context-free grammar for which every valid string has a unique leftmost derivation or parse tree.

### What is Chomsky classification of grammar?

Most famous classification of grammars and languages ??introduced by Noam Chomsky is divided into four classes: Recursively enumerable grammars –recognizable by a Turing machine. Context-sensitive grammars –recognizable by the linear bounded automaton. Context-free grammars - recognizable by the pushdown automaton.

#### How do you remove ambiguity?

There exists no general algorithm to remove the ambiguity from grammar. To check grammar ambiguity, we try finding a string that has more than one parse tree. If any such string exists, then the grammar is ambiguous otherwise not.

**You May Like Also**