Mandatory and optional spaces - parsing

Question

I need to parse strings like this:
"qqq www eee" -> "qqq", "www", "eee" (case A)
"qqq www eee" -> "qqq", "www", "eee" (case B)
Here's the grammar I currently have:
grammar Query;
SHORT_NAME : ('a'..'z')+ ;
name returns [String s]: SHORT_NAME { $s = $SHORT_NAME.text; };
names
returns [List<String> v]
#init { $v = new ArrayList<String>(); }
: name1 = name { $v.add($name1.s); }
(' ' name2 = name { $v.add($name2.s); })*;
It works fine for caseA, but fails for caseB:
line 1:4 missing SHORT_NAME at ' '
line 1:5 extraneous input ' ' expecting SHORT_NAME
line 1:10 extraneous input ' ' expecting SHORT_NAME
Any ideas how to make it work?

Answer 1

Remove the literal ' ' from your names rule and replace it with a SPACES token:
grammar Query;
SPACES
: (' ' | '\t')+
;
SHORT_NAME
: ('a'..'z')+
;
name returns [String s]
: SHORT_NAME { $s = $SHORT_NAME.text; }
;
names returns [List<String> v]
#init { $v = new ArrayList<String>(); }
: a=name { $v.add($a.s); } (SPACES b=name { $v.add($b.s); })*
;
Or simply discard the spaces at the lexer-level so that you don't need to put them in your parser rules:
grammar Query;
SPACES
: (' ' | '\t')+ {skip();}
;
SHORT_NAME
: ('a'..'z')+
;
name returns [String s]
: SHORT_NAME { $s = $SHORT_NAME.text; }
;
names returns [List<String> v]
#init { $v = new ArrayList<String>(); }
: (name { $v.add($b.s); })+
;