How do I use %empty correctly? - parsing

Question

I'm new to bison/fex and I am trying to recognize patterns of 1-3 words of input.
My .l recognizes WORD as any series of lowercase characters, treats % and $ characters as tokens of their own ascii value, ignores whitespace, and recognizes everything else as an ERR token.
MISC [\%\$]
%%
[a-z]+ { yylval.WORD = yytext; return WORD; }
[ \t\r\n]+ {} //ignore whitespace
{MISC} return (int) yytext[0];
. return ERR; //unrecognized input
My .y tries to recognize sequences of 1-3 WORDS separated by characters % and $. I want it so that even if I input just 1 WORD, I still get a complete statement. I don't include any rules for the ERR token to invoke a syntax error in the parser when an unrecognize character is received as input.
%{
#include <stdio.h>
int yylex();
void yyerror(char* s){
fprintf(stderr, "%s\n", s);
};
%}
%define api.value.type union
%token <char*> WORD
%nterm <char*> word1 word2 word3
%token ERR
%%
statement: word1 word2 word3 { printf("%s, %s, %s\n", $1, $2, $3); return 0; }
;
word1: WORD { $$ = $1; }
;
word2: %empty { $$ = "nothing"; }
| '%' WORD { $$ = $2; }
;
word3: %empty { $$ = "nothing";}
| '$' WORD { $$ = $2; }
;
%%
My main.c loops on yyparse(). Ideally I'm trying to parse only 1 line of input per iteration.
#include <unistd.h>
#include <stdio.h>
int yyparse();
int yylex();
extern FILE* yyin;
extern void yyrestart();
int main() {
while(1) {
printf("input: ");
if (yyparse() == 0) {
printf("success\n");
};
yyrestart(yyin);
}
return 0;
}
However, I am getting adverse output, and I can't explain what's causing it:
In: word word -> Out: word word, nothing, nothing
In: word word word -> Out: word word, nothing, nothing
In: word % word $ word -> Out: word % word $ word, word $ word, word
Additionally, if I input only 1 WORD, my command line hangs until it receives additional input. This additional input could be anything. Even characters that would normally be recognized as an ERR token and invoke a syntax error somehow get by.
In: word. -> Out: word., nothing, nothing
I want my parser to be able to run even if I give it only 1 word of input. I thought that with the inclusion of %empty for subrules word2 and word3 I would get this behavior, but I am not sure what I am doing wrong.