=== Result
echo -n "bbaca" | ./a.out 
[A] -> a
[B] -> b
[A] -> B
[A] -> a
[B] -> b c
[A] -> B

=== grammar

%{

#include <stdio.h>
#define YYSTYPE char const *
int yylex (void);
void yyerror (char const *);

%}

%start start

%glr-parser

%%

start: A

A
	: 'a' { printf ("[A] -> a\n"); }
	| B   { printf ("[A] -> B\n"); }

B
	: 'b' A       %dprec 1 { printf ("[B] -> b\n"); }
	| 'b' A 'c' A %dprec 2 { printf ("[B] -> b c\n"); }
  ;

%%

void yyerror(const char *str)
{
    fprintf(stderr, "yyerror: %s\n", str);
}

int yywrap(){}

int main()
{
    return yyparse();
}

=== lexer

%%

a	{ return 'a'; }
b   { return 'b'; }
c   { return 'c'; }

%%