antlr rewriting output of a rule

问题:

I am trying to write an antlr script where in, rule1 has a subrule , rule2. I am using StringTemplate on rule 1.

What I want to do, is restructure the text matched by rule2 before it is consumed/used by rule1. How do I do that ?

options{
output=template;
}

rule1 :
  begin sub-rule2 end ';' -> meth(body={rule1.text})

sub-rule2 :
   sub-rule3
 | sub-rule4
 | sub-rule5;

here "meth" is the stringtemplate call

If say sub-rule 4 matches "select * from dual;", I would like this to be passed to rule1 "#sql (select * from dual);".

Here is my Actual code I would like the statements matched by the select_statement rule to be wrapped in '#sql()' and to be passed in "stats" list to the "body" attribute of the "meth" template :

body 
@init {
      List stats = new ArrayList();
    }   :   
    BEGIN s=statement{ stats.add($s.text); } SEMI ( s=statement{ stats.add($s.text); } SEMI | pragma SEMI )*
    ( EXCEPTION exception_handler+ )? END ID? -> method(modifiers={"public"},returnType={"void"},name={"execute"},body={stats})
    ;


statement :
    label*
    ( assign_or_call_statement
    | case_statement
    | close_statement
    | continue_statement
    | basic_loop_statement
    | execute_immediate_statement
    | exit_statement
    | fetch_statement
    | for_loop_statement
    | forall_statement
    | goto_statement
    | if_statement
    | null_statement
    | open_statement
    | plsql_block
    | raise_statement
    | return_statement
    | sql_statement 
    | while_loop_statement
    ) 
    ;

    sql_statement
    : (commit_statement
    | delete_statement
    | insert_statement
    | lock_table_statement
    | rollback_statement
    | savepoint_statement
    | select_statement 
    | set_transaction_statement
    | update_statement )
    ;


    select_statement :
        SELECT swallow_to_semi 
    ;

    SELECT  :   'select';

    swallow_to_semi :
        ~( SEMI )+
    ;

回答1:

You can specifically define what a rule can return like this:

sub_rule2 returns [String x] 
  :  sub_rule3 {$x = ... }
  |  sub_rule4 {$x = "#sql (" + $sub_rule4.text + ");";}
  |  sub_rule5 {$x = ... }
  ;

Now sub_rule2 returns a String x which you can use like this:

rule1
  :  ... sub_rule2 ... -> meth(body={sub_rule2.x})
  ;

Note the sub_rule2.x.

EDIT

You could also create a custom method that checks if the text to be added to the List starts with "select " like this:

grammar YourGrammarName;

options{
  output=template;
}

@parser::members {
  private void addStat(String stat, List<String statList>) {
    // 1. if `stat` starts with "select ", wrap "#sql(...)" around it.
    // 2. add `stat` to `statList`
  }
}

body 
@init {
  List<String> stats = new ArrayList<String>();
}   
  :  BEGIN s=statement { addStat($s.text, stats); } SEMI 
     ( s=statement     { addStat($s.text, stats); } SEMI 
     | pragma                                      SEMI
     )*
     (EXCEPTION exception_handler+)? END ID? 

     -> method(modifiers={"public"},returnType={"void"},name={"execute"},body={stats})
  ;