Question

I need a small trick to get my parser completely working.
I use antlr to parse boolean queries.

a query is composed of elements, linked together by ands, ors and nots.

So I can have something like :

"(P or not Q or R) or (( not A  and B) or C)"

Thing is, an element can be long, and is generally in the form :

a an_operator b

for example :

"New-York matches NY"

Trick, one of the an_operator is “not like”

So I would like to modify my lexer so that the not checks that there is no like after it, to avoid parsing elements containing “not like” operators.

My current grammar is here :

// save it in a file called Logic.g
grammar Logic;

options {
  output=AST;
}

// parser/production rules start with a lower case letter
parse
  :  expression EOF!    // omit the EOF token
  ;

expression
  :  orexp
  ;

orexp
  :  andexp ('or'^ andexp)*    // make `or` the root
  ;

andexp
  :  notexp ('and'^ notexp)*      // make `and` the root
  ;

notexp
  :  'not'^ atom    // make `not` the root
  |  atom
  ;

atom
  :  ID
  |  '('! expression ')'!    // omit both `(` andexp `)`
  ;

// lexer/terminal rules start with an upper case letter
ID    : ('a'..'z' | 'A'..'Z')+;
Space : (' ' | '\t' | '\r' | '\n')+ {$channel=HIDDEN;};

Any help would be appreciated.
Thanks !

Answer 1

Here’s a possible solution:

grammar Logic;

options {
  output=AST;
}

tokens {
  NOT_LIKE;
}

parse
  :  expression EOF!
  ;

expression
  :  orexp
  ;

orexp
  :  andexp (Or^ andexp)*
  ;

andexp
  :  fuzzyexp (And^ fuzzyexp)*
  ;

fuzzyexp
  :  (notexp -> notexp) ( Matches e=notexp  -> ^(Matches $fuzzyexp $e)
                        | Not Like e=notexp -> ^(NOT_LIKE $fuzzyexp $e)
                        | Like e=notexp     -> ^(Like $fuzzyexp $e)
                        )?
  ;

notexp
  :  Not^ atom
  |  atom
  ;

atom
  :  ID
  |  '('! expression ')'!
  ;

And     : 'and';
Or      : 'or';
Not     : 'not';
Like    : 'like';
Matches : 'matches';
ID      : ('a'..'z' | 'A'..'Z')+;
Space   : (' ' | '\t' | '\r' | '\n')+ {$channel=HIDDEN;};

which will parse the input "A not like B or C like D and (E or not F) and G matches H" into the following AST: