/* file y.y */
/* $ YACC=bison make y # build */
/* $ bison y.y && gcc -g -Wall y.tab.c && echo bababa | ./a.out #
alternative */
/* $ echo ababbb ./y # use */
%glr-parser
%{
# include<stdio.h>
void yyerror(const char*a) {
fprintf(stderr, "\n%s\n", a);
}
int yylex(void) {
return getchar();
}
%}
%%
a0: a4 a1 a5 '\n' ;
a1: a2 a3 | a3 a2 ;
a2: a4 a4 | a5 a5 ;
a3: a4 a5 | a5 a4 ;
a4: 'a' ;
a5: 'b' ;
%%
int main() {
return yyparse();
}
#if 0
Given example
0: 4 1 5
1: 2 3 | 3 2
2: 4 4 | 5 5
3: 4 5 | 5 4
4: "a"
5: "b"
ababbb
bababa
abbbab
aaabbb
aaaabbb
|Date: Tue, 29 Dec 2020 12:43:11 +0000
|From: "'Mike Day' via Chat" <[email protected]>
|To: [email protected]
|Subject: Re: [Jchat] https://adventofcode.com/2020/day/19
|Message-ID: <[email protected]>
|Content-Type: text/plain; charset=utf-8
|
|This partial copy from (my) part 2 might provide enough insight:
|<<--- Part Two ---
|
|As you look over the list of messages, you realize your matching rules
aren't quite right. To fix them, completely replace rules 8: 42 and 11: 42
31 with the following:
|
|8: 42 | 42 8
|11: 42 31 | 42 11 31
|This small change has a big impact: now, the rules do contain loops, and
the list of messages they could hypothetically match is infinite. You'll
need to determine how these changes affect which messages are valid...... >>
|
|So these two rules become self referential.
|
|I’ve no Idea what David’s talking about!
|
|Cheers,
|
|M
#endif
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