Bison Daily News: Your Quick Guide to Everything Bison!

Okay, so today I dug into Bison. It was a bit of a head-scratcher at first, but I think I’ve got a handle on the basics now. Here’s how my day went down.

Getting Started with Bison

First things first, I needed to actually install Bison. I’m on a Debian-based system, so it was pretty straightforward:

I simply used sudo apt-get install bison. It automatically installs Bison and any dependent tools.

After that, I wanted to make sure everything was set up correctly. So I just typed bison --version into the terminal, and boom, it showed me the version number. All good there.

My First Bison Project (a super simple calculator)

I figured the best way to learn was by doing. I decided to build a really, really simple calculator. One that could just handle addition and subtraction. Nothing fancy, just to get my feet wet.

I created a file called calculator.y. This is where the Bison “grammar” goes. It’s like defining the rules of your language (in this case, the calculator language).

Here’s the rough draft of what I put in it:

#include 
#include 
int yylex(void);
void yyerror(const char s);


%token NUMBER
%left '+' '-'

program:
expression

printf("Result: %dn", $1);


expression:
expression '+' expression { $$ = $1 + $3; }
 expression '-' expression { $$ = $1 - $3; }

 NUMBER { $$ = $1; }


void yyerror(const char s) {
fprintf(stderr, "Error: %sn", s);
exit(1);

int main() {
yyparse();
return 0;

I also needed a “lexer”. Think of it like a word recognizer. Bison focuses on the structure of the input, but the lexer is what breaks the input down into individual “tokens” (like numbers and operators). I used Flex for this, since it plays nicely with Bison.

I made a file named calculator.l:

#include "*.h"


[0-9]+      { yylval = atoi(yytext); return NUMBER; }
"+"         { return '+'; }
"-"         { return '-'; }
[ tn]     ; / Ignore whitespace /
.           { yyerror("Invalid character"); }

int yywrap() {

return 1;

Compiling and Running

This was the moment of truth. I had to run a few commands to get everything compiled:

• bison -d calculator.y (This generates *.c and *.h)
• flex calculator.l (This creates *.c)
• gcc *.c *.c -o calculator (This compiles everything into an executable)

After that I just type ./calculator to my terminal!

I typed in 5 + 3, hit enter, and… it printed “Result: 8”! Holy cow, it actually worked! Then I tried 10 - 2, and yep, “Result: 8” again. Felt like a total coding wizard.

Troubleshooting and Headaches

Of course, it wasn’t all smooth sailing. I spent a good chunk of time just staring at error messages, trying to figure out what I’d messed up. Most of the time, it was something silly, like a missing semicolon or a typo in the grammar rules. The error messages from Bison can be a bit cryptic, but with enough squinting and Googling, I usually managed to figure it out.

It spent almost half of my time to debug, and the previous code is the lastest version.

What I Learned (and What’s Next)

So, what did I get out of all this? Well, I definitely have a better understanding of how parsers work. It’s like learning the underlying structure of a language, which is pretty cool. Bison is powerful, but it’s also got a steep learning curve. I’ve only scratched the surface. I think the best way to learn, for me, it is going through those examples, I will do more practice.

Next, I want to try adding multiplication and division to my calculator. Maybe even parentheses! And then… who knows? Maybe I’ll try building a parser for a simple programming language. It’s a long road, but today was a good first step.