## What is Bottom-up Parsing?

Updated on 29-Oct-2021 07:03:53
Bottom-up parsing can be represented as an attempt to reduce the input string ω to the start symbol of a grammar by discovering out the right-most derivation of ω in reverse. This is similar to generating a parse tree for the input string ω by starting with leaves and proceeding toward the root i.e., attempting to generate the parse tree from the bottom-up.This contains searching for the substring that connect the right side of any of the production of the grammar. This substring is restored by the left-hand side nonterminal of the production if this replacement leads to the generation ... Read More

## What is Top-Down Parsing?

Updated on 29-Oct-2021 06:59:41
In top-down parsing, the parse tree is generated from top to bottom, i.e., from root to leaves & expand till all leaves are generated.It generates the parse tree containing root as the starting symbol of the Grammar. It starts derivation from the start symbol of Grammar & performs leftmost derivation at each step.Drawback of Top-Down ParsingTop-down parsing tries to identify the left-most derivation for an input string ω which is similar to generating a parse tree for the input string ω that starts from the root and produce the nodes in a pre-defined order.The reason that top-down parsing follow the ... Read More

## What are Parsing Techniques in Compiler Design?

Updated on 29-Oct-2021 06:57:11
Parsing is known as Syntax Analysis. It contains arranging the tokens as source code into grammatical phases that are used by the compiler to synthesis output generally grammatical phases of the source code are defined by parse tree. There are various types of parsing techniques which are as follows −Top-Down ParserIt generates the Parse Tree from root to leaves. In top-down parsing, the parsin begins from the start symbol and changes it into the input symbol.An example of a Top-Down Parser is Predictive Parsers, Recursive Descent Parser.Predictive Parser − Predictive Parser is also known as Non-Recursive Predictive Parsing. A predictive ... Read More

## What is Parsers?

Updated on 29-Oct-2021 06:54:33
Syntax Analysis or Parser is the second phase of compilation. The parser takes as its input tokens generated from the previous phase, i.e., the Lexical Analyzer phase, and groups them in such a way that their syntax can be recognized.It takes input as tokens & converts them into Parse Tree.Example1 − Statement a = b + c will be converted to a sequence of tokens a, b, c, =, +, and these tokens will be converted to Parse Tree by Parser. The corresponding Parse Tree will be generated as −Example2 − Draw Parse Tree for the statement. (If A = ... Read More

## What is the role of the lexical analyzer in compiler design?

Updated on 29-Oct-2021 06:51:25
The lexical analysis is the first phase of the compiler where a lexical analyser operate as an interface between the source code and the rest of the phases of a compiler. It reads the input characters of the source program, groups them into lexemes, and produces a sequence of tokens for each lexeme. The tokens are sent to the parser for syntax analysis.If the lexical analyzer is located as a separate pass in the compiler it can need an intermediate file to locate its output, from which the parser would then takes its input. It can eliminate the need for ... Read More

## What is Ambiguous Grammar?

Updated on 26-Oct-2021 08:59:12
A Grammar that makes more than one Leftmost Derivation (or Rightmost Derivation) for the similar sentence is called Ambiguous Grammar.Example − Verify whether the following Grammar is Ambiguous or Not.E → E+E|E $\ast$ E|idSolutionFor string id + id * id, there exist two parse trees.E ⇒lm $\underline{E}$+E ⇒ id+ $\underline{E}$⇒ id+$\underline{E}$ $\ast$ E⇒ id+id $\ast$ $\underline{E}$⇒ id+id $\ast$ idE ⇒lm $\underline{E}$ $\ast$ E⇒ $\underline{E}$+E $\ast$ E⇒ id+ $\underline{E}$ $\ast$ E⇒ id+id $\ast$ $\underline{E}$⇒ id+id $\ast$ idSo, the same string is generated using two different leftmost derivations. Each is having a different parse tree.∴ Two different parse trees exist for string id + id ... Read More

## What are Parse Trees (Derivation Trees)?

Updated on 26-Oct-2021 08:47:49
Derivations mean replacing a given string’s non-terminal by the right-hand side of the production rule. The sequence of applications of rules that makes the completed string of terminals from the starting symbol is known as derivation. The parse tree is the pictorial representation of derivations. Therefore, it is also known as derivation trees. The derivation tree is independent of the other in which productions are used.A parse tree is an ordered tree in which nodes are labeled with the left side of the productions and in which the children of a node define its equivalent right parse tree also known ... Read More

## What are Derivations?

Updated on 26-Oct-2021 08:38:45
Derivations mean replacing a given string’s non-terminal by the right-hand side of the production rule. The sequence of applications of rules that makes the completed string of terminals from the starting symbol is known as derivation.It can derive terminal strings, beginning with the start symbol, by repeatedly replacing a variable with some production. The language of CFG is a set of terminal symbols we can derive so. This language is called context Free Language.Derivations are denoted by ⇒.For example, consider a Grammar.G=({S}, {a, b}, P, S), where, P contains following productions −P={S→aSa |bSb | ∈}In the above, S may be ... Read More

## What is Context-Free Grammar?

Updated on 26-Oct-2021 08:20:44
Grammar − It is a set of rules which checks whether a string belongs to a particular language a not.A program consists of various strings of characters. But, every string is not a proper or meaningful string. So, to identify valid strings in a language, some rules should be specified to check whether the string is valid or not. These rules are nothing but make Grammar.Example − In English Language, Grammar checks whether the string of characters is acceptable or not, i.e., checks whether nouns, verbs, adverbs, etc. are in the proper sequence.Context-Free GrammarIt is a notation used to specify ... Read More

## What is the implementation of a Lexical Analyzer?

Updated on 26-Oct-2021 08:18:10
Lexical Analysis is the first step of the compiler which reads the source code one character at a time and transforms it into an array of tokens. The token is a meaningful collection of characters in a program. These tokens can be keywords including do, if, while etc. and identifiers including x, num, count, etc. and operator symbols including >, >=, +, etc., and punctuation symbols including parenthesis or commas. The output of the lexical analyzer phase passes to the next phase called syntax analyzer or parser.The syntax analyser or parser is also known as parsing phase. It takes tokens ... Read More