Add support for line breaks and grouping

[audio-engineer]

@Zeta611 Cool package! I really like the design, but I found two bugs/suggestions:

1. It would be great if rows could be inserted that are not productions, i.e., don't require ::= and a RHS. Those rows could be used to write comments like "Arithmetic expressions" to group the following productions together. Basically like the first column in the current setup but without the other columns.
2. There is no option to force a line break to split a long production into multiple lines. This results in render issues like this one:

One solution would be to add another delimiter, e.g., `\\` that can be added on the RHS to force a new line without adding `|`, but keeping the continuation of the production right under the beginning of the RHS on the previous line.

[Zeta611]

Thanks for the feedback! Both of your suggestions would indeed be useful. I'll try to work on it when I find the time to do it.

[audio-engineer]

@Zeta611 Sounds great!

I got a few more suggestions that are related:

3. RHS overflows on the right on long productions, but a BNF can be long and overflow at the bottom of the page. You are using tabularray and could add an option to pass long to tabularray to create a multi-page BNF that only splits between two productions, not e.g., two alternatives or line splits (from suggestion 2.) of the same production.
4. Again, since you are using tabularray it would be cool if it was possible to pass options like label and caption to caption the BNF without having to use a figure environment.

[Zeta611]

All sounds useful! If you don't mind, can you share the MWE source to typeset the grammar in the screenshot?

[audio-engineer]

@Zeta611 Sure I can, will do it later

[audio-engineer]

@Zeta611 Here you go. This MWE overflows less than then one in the screenshot because I cut out all the production rules above and below the ones you see in the screenshot.
Still, it should be good enough to understand the issue.

\documentclass{article}

\usepackage[a4paper]{geometry}
\usepackage{simplebnf}

\SetBNFConfig{
comment = {~}
}
\SetBNFLayout{
colspec = {llcl},
column{1} = {font = \sffamily},
column{2} = {font = \ttfamily},
column{4} = {font = \ttfamily},
column{5} = {font = \sffamily}
}

\begin{document}
\begin{bnf}(
prod-sep = 5pt
)
<if-stmt> ~ If Statement ::= IF LPAREN <expr> RPAREN <stmt-list> [ ELSE <stmt-list> ] ENDIF
;;
<for-stmt> ~ For Statement ::= FOR LPAREN <stmt> SEMICOLON <expr> SEMICOLON <var-assign-stmt> RPAREN <stmt-list> ENDFOR
;;
<while-stmt> ~ While Statement ::= WHILE LPAREN <expr> RPAREN <stmt-list> ENDWHILE
;;
<loop-stmt> ~ Loop ::= <for-stmt>
| <while-stmt>
\end{bnf}
\end{document}

[audio-engineer]

@Zeta611 Might also be of interest: Due to the bug I temporarily switched to using the tblr for my EBNF. I will not post the whole code since it's just a plain table with colspec = {llcX} and some font config, but here is the part with the long production rules again, adjusted for tblr:

{ Logical \\ Expression } & <logic-expr> & = & { BOOLEAN \\
| <rel-expr> \\
| NOT <logic-expr> \\
| <logic-expr> AND <logic-expr> \\
| <logic-expr> OR <logic-expr> ;} \\
Expression & <expr> & = & { <arith-expr> \\
| <rel-expr> \\
| <logic-expr> \\
| STRING ;} \\
{ If \\ Statement } & <if-stmt> & = & IF LPAREN <expr> RPAREN <stmt-list> [ ELSE <stmt-list> ] ENDIF ; \\
{ For \\ Statement } & <for-stmt> & = & FOR LPAREN <stmt> SEMICOLON <expr> SEMICOLON <var-assign-stmt> RPAREN <stmt-list> ENDFOR ; \\
{ While \\ Statement } & <while-stmt> & = & WHILE LPAREN <expr> RPAREN <stmt-list> ENDWHILE ; \\
Loop & <loop-stmt> & = & <for-stmt> | <while-stmt> ; \\

This gives me a nice:

It would be cool to be able to achieve something like this with your package + some of the other suggestions that I mentioned, like "group title rows", etc. 💯

[Zeta611]

Thanks for the comprehensive example and suggestions!

---

• I'm also planning to back-port this into using "legacy" backends like tabular + multirow + etc., due to restrictions of TAPS. I can't use my own package due to this, which is ironic. I'll be able to start working on these improvements until next Thursday!

[audio-engineer]

That sounds great. Let me know if you need more assistance 👍