Lexer Part of Anglr File

Introduction

A lexical analyser is that part of the text analyser (e.g. the compiler) that transmits terminal symbols to the syntax analyser. It's composed from any number of scanners. One of them must be an initial scanner and must never be removed from the stack unless it is replaced immediately by another scanner.

Syntax

The syntax of the lexical part is very simple. It has no content. The list of scanners it needs for its operation is defined by attributes. The followining syntax rule defines the structure of lexer part:

RULE L-1

<lexer part>
    : <attribute list> ? '%lexer' <identifier> '%{' <attribute list> ? '%}'
    ;
                    

Here is an example of lexer part:

[ Description Text='Lexer for anglr file' Hover='true' ]
[
    UseScanner
        ScannerId='commentScanner'
        InitialScanner='mathScanner'
        Hover='true'
]
[ CompilationInfo ClassName='MathLexer' NameSpace='Math.Lexer' Access='public' Hover='true' ]
%lexer mathLexer
%{

%}
                    

Discussion

RULE L-1 - Structure of lexer part

Rule RULE L-1 defines the structure of the lexer part:

• Lexer part is preceded by possibly empty attribute list
• attribute list is followed by reserved word %lexer and an identifier representing the name of lexer
• Then there is another possibly empty list of attribute list between part parentheses %{ ad %}.

In example above lexer part is preceded by this attribute list:

[ Description Text='Lexer for anglr file' Hover='true' ]
[
    UseScanner
        ScannerId='commentScanner'
        InitialScanner='mathScanner'
        Hover='true'
]
[ CompilationInfo ClassName='MathLexer' NameSpace='Math.Lexer' Access='public' Hover='true' ]
                    

Name of lexer part is:

%lexer mathLexer
                    

and its body is empty:

%{

%}
                    

Attributes

The list of attributes specified before the lexical part must contain attributes describing which scanners contain the lexical analyser. Attributes located between %{ and %} are not important.

These attributes are mandatory for lexer part: