Antlr4 - Parser for multi line file -

Question

I'm trying to use antlr4 to parse a ssh command result, but I can not figure out why this code doesn't work, I keep getting an "extraneous input" error.

Here is a sample of the file I'm trying to parse :

system
home[1]  HOME-NEW
    sp
    cpu[1]
    cpu[2]
home[2]  SECOND-HOME
    sp
    cpu[1]
    cpu[2]

Here is my grammar file :

listAll 
  : ( system | home | NL)*
  ;

elements
  : (sp | cpu )*
  ;

home 
  : 'home['  number ']' value NL elements
  ;

system
  : 'system' NL
  ;

sp 
  : 'sp' NL
  ;

cpu
  : 'cpu[' number ']' NL
  ;

value 
  : VALUE
  ;

number
  : INT
  ;

VALUE : STRING+; 
STRING: ('a'..'z'|'A'..'Z'| '-' | ' ' | '(' | ')' | '/' | '.' | '[' | ']');
INT   :    ('0'..'9')+ ;
NL  : '\r'? '\n';
WS    :     (' '|'\t')* {skip();} ;

The entry point is 'listAll'. Here is the result I get :

(listAll \r\n (system system \r\n) home[1]  HOME-NEW \r\n sp \r\n cpu[1] \r\n cpu[2] \r\n[...])

The parsing failed after 'system'. And I get this error : line 2:1 extraneous input 'home[1] HOME-NEW' expecting {, system', NL, WS}

Does anybody know why this is not working ? I am a beginner with Antlr, and I'm not sure I really understand how it works ! Thank you all !

Answer 1

You need to combine NL and WS as one WS element and skip it using -> skip (not {skip()} )

And since the WS will be skipped automatically, no need to specify it in all the rules.

Also, your STRING had a space ( ' ' ) which was causing the error and taking up the next input.

Here is your complete grammar :

listAll   :   ( system | home )* ;

elements  :   ( sp | cpu )* ;

home      :   'home['  number ']' value elements;

system    :   'system' ;

sp        :   'sp' ;

cpu       :   'cpu[' number ']' ;

value     :   VALUE ;

number    :   INT ;

VALUE     :   STRING+; 

STRING    :   ('a'..'z'|'A'..'Z'| '-' | '(' | ')' | '/' | '.' | '[' | ']') ;

INT       :   [0-9]+ ;

WS        :   [ \t\r\n]+ -> skip ;

Also, I'll suggest you to go through the ANTLR4 Documentation