YACC nothing

[HarryAnkers]

is there a way for you to have an option of matching a nothing case in yacc.
for example:
A : B C B
C : SOMETHING
|

Or would I have to do
A : B C B
| B B
C : SOMETHING

[fyquah]

What you need might be empty rules

I found out about that by googling "Empty sequence" on google, which yields me this stackoverflow post.

[m8pple]

(I responded to this via email on the 13th, but it doesn't seem to have shown up here.
Usually GH reflects them back up as issues if you respond.)

---

In bison there is a special token called %epsilon, which can be used
to explicitly mark something as empty-by-intent:

https://www.gnu.org/software/bison/manual/html_node/Empty-Rules.html

C : SOMETHING
| %empty

There is then some nice stuff which will warn you if you declare a production empty, but it isn't.

Doesn't work in classic yacc though, or older versions of bison.
However, you can define a symbol called epsilon:

epsilon : /* I am empty */

then use it in your grammar:

C : SOMETHING
| epsilon