Record the types of a comma seperated list of identifiers?

Question

For semantic analysis I need to put the identifiers and their types into a custom Hash Map. But given the following grammar rules and implementation it is beyond me how I could record all identifiers declared by the ident_list below.

Grammar rules:

var_decl := var ident_list:type ( , ident_list:type )* ; 
ident_list := identifier ( , identifier )*
type := integer | boolean | real | string | void

The implementation in the jjt file is as follows:

void var_decl() #void : {Token t; String[] name;}
{
  <VAR> ident_list() <COLON> type() #var_decl(2) 
    (<COMMA> ident_list() <COLON> type() #var_decl_ext(2))* <SEMIC>
}


void ident_list() : {}
{
  identifier() (<COMMA> identifier())*
}


String identifier() #ID : { Token t; }
{
  t=<ID> { jjtThis.value = t.image; return t.image; }
}


String type() #TYPE : { Token t; }
{
  t=<INTEGER> {jjtThis.value = t.image; return t.image; } |
  t=<BOOLEAN> {jjtThis.value = t.image; return t.image; } |
  t=<REAL> {jjtThis.value = t.image; return t.image; } |
  t=<STRING> {jjtThis.value = t.image; return t.image; } |
  t=<VOID> {jjtThis.value = t.image; return t.image; }
}

If it were just a singular identifier in each var_decl I can see how to get the necessary information, but how would you pass a list of one or more identifiers back up to var_decl for assignment? Is this realistically achievable in jjtree/javacc?

Answer 1

Yes. You can return a list of identifiers from ident_list like this:

List<String> ident_list() : {
    List<String> ids = new ArrayList<String>() ;
    String id ; }
{
  id = identifier() { ids.add(id) ; }
  (<COMMA> id = identifier() { ids.add(id) ; } )*
  {return ids ; }
}

Now refactor var_decl a bit. What you do with the map is up to you, but I would stash it in in a node.

void var_decl() #var_decl : {
    HashMap<String, String> decls = new HashMap<String, String>() ;
}
{
  <VAR> one_var_decl(decls)
  ( <COMMA> one_var_decl(decls) )* <SEMIC>
  { jjThis.decls = decls ; }
}

And build the map in the new nonterminal.

void one_var_decl(HashMap<String, String> decls) #void :
{
    List<String> ids ;
    String ty ;
}
{
    ids = ident_list() <COLON> ty = type()
    { for( String id <- ids ) {
           // You may want to emit an error or warning here if there is a duplication.
           decls.add(id, ty) ; } }
}