What is a lexer generator?
Lex is a program designed to generate scanners, also known as tokenizers, which recognize lexical patterns in text. Lex is an acronym that stands for “lexical analyzer generator.” It is intended primarily for Unix-based systems.
What is the difference between lexer and parser?
A lexer and a parser work in sequence: the lexer scans the input and produces the matching tokens, the parser then scans the tokens and produces the parsing result.
What is the benefit of using a lexer before a parser?
The iterator exposed by the lexer buffers the last emitted tokens. This significantly speeds up parsing of grammars which require backtracking. The tokens created at runtime can carry arbitrary token specific data items which are available from the parser as attributes.
What does a Lexer do?
The lexer just turns the meaningless string into a flat list of things like “number literal”, “string literal”, “identifier”, or “operator”, and can do things like recognizing reserved identifiers (“keywords”) and discarding whitespace. Formally, a lexer recognizes some set of Regular languages.
What is lexeme in compiler?
A lexeme is a sequence of characters in the source program that matches the pattern for a token and is identified by the lexical analyzer as an instance of that token.
What is the purpose of a lexer?
A lexer will take an input character stream and convert it into tokens. This can be used for a variety of purposes. You could apply transformations to the lexemes for simple text processing and manipulation. Or the stream of lexemes can be fed to a parser which will convert it into a parser tree.
What is a lexer used for?
Which is the tool for parser generator?
YACC is an automatic tool that generates the parser program.
What is the input to a parser generator?
A parser generator is an application which generates a parser. Sometimes also called a ‘compiler compiler’. The usual input is a formal specification of the grammar the parser has to recognize, plus code implementing the actions the parser has to take when recognizing the various parts of its input.
How does lexer and parser communicate?
Communication between lexer and parser
- The lexer eagerly converts the entire input string into a vector of tokens.
- Each time the lexer finds a token, it invokes a function on the parser, passing the current token.
- Each time the parser needs a token, it asks the lexer for the next one.