Generating a vigenere square in LaTeX3

Question

I'm trying to generate a vigenere square using expl3. My aim is to provide an easy interface for different alphabets and different scaling. Therefore I chose a tabular-based approach which seemed very easy to customize.

Points I would especially appreciate feedback to:

• Is using tabular a good idea or might it be very bad (e.g. when the user customizes array stretches)?
• Am I abusing expl3 at any point (local vs. global)?
• the user interface in general (key-value approach)

Code:

\documentclass{article}
\usepackage[landscape]{geometry}
\usepackage{xparse}
\ExplSyntaxOn
\keys_define:nn { vigenere }
 {
 font .code:n = { \cs_set_eq:NN \__vigenere_font: #1 },
 font .default:n = { \small },
 font .initial:n = { \small },
 tabcolsep .dim_set:N = \l__vigenere_tabcolsep_dim,
 tabcolsep .initial:n = { 3pt },
 alphabet .tl_set:N = \l__vigenere_alphabet_tl,
 alphabet .initial:n = { A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z }
 }
\NewDocumentCommand { \printvigeneretabular } { O{} }
 {
 \group_begin:
 \keys_set:nn { vigenere } { #1 }
 \clist_set:NV \l_tmpa_clist \l__vigenere_alphabet_tl
 \clist_clear:N \l_tmpb_clist
 \tl_clear:N \l_tmpa_tl
 \int_step_inline:nnnn { 1 } { 1 } { \clist_count:N \l_tmpa_clist }
 {
 \tl_put_right:Nx \l_tmpa_tl { c| }
 }
 \__vigenere_font:
 \dim_set_eq:NN \tabcolsep \l__vigenere_tabcolsep_dim
 \expandafter\tabular\expandafter{\expandafter|\l_tmpa_tl}
 \hline
 \bool_while_do:nn { \int_compare_p:n { \clist_count:N \l_tmpa_clist > 0 } }
 {
 \clist_use:Nnnn \l_tmpa_clist { & } { & } { & }
 \clist_if_empty:NF \l_tmpb_clist
 { & \clist_use:Nnnn \l_tmpb_clist { & } { & } { & } }
 \clist_gpop:NN \l_tmpa_clist \l_tmpa_tl
 \clist_gput_right:NV \l_tmpb_clist \l_tmpa_tl
 \\\hline
 }
 \endtabular
 \group_end:
 }
\ExplSyntaxOff
\begin{document}
	\printvigeneretabular\par
	\printvigeneretabular[font=\tiny,alphabet={1,2,3,4,5,6,7,8,9,10},tabcolsep=1pt]
\end{document}

Answer 1

About your points:

1. The interface seems pretty clear.

2. If you fear about the \arraystretch parameter being abused, you're right: on a double spaced document all tables come out horribly and local remedies are often necessary. Maybe adding a stretch key could help for these cases.

3. Yes, you're abusing local and global assignments.

Some comments about the code:

1. There is no point in the key alphabet to set a tl variable, which is then converted to a clist

2. There's no need to set a .default:n for the font key: the value specified with .default:n would be used if the key is called without assigning a value

3. \int_step_inline:nnnn can be done more simply using the * feature of tabular

4. Never use \expandafter in expl3 code

5. You should not use global assignments on local variables

6. \clist_gpop:NN should be \clist_gpop_left:NN (but I changed it into \seq_pop_left:NN)

7. One can do with a simpler loop, using \prg_replicate:nn

I'd also prefer to prepare the table body outside the table, with sequences instead of clists, which are less efficient.

\documentclass{article}
\usepackage[landscape]{geometry}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand { \printvigeneretabular } { O{} }
 {
 \vigenere_tabular:n { #1 }
 }
% keys
\keys_define:nn { vigenere }
 {
 font .code:n = { \cs_set_eq:NN \__vigenere_font: #1 },
 font .initial:n = { \small },
 tabcolsep .dim_set:N = \l__vigenere_tabcolsep_dim,
 tabcolsep .initial:n = { 3pt },
 alphabet .clist_set:N = \l__vigenere_alphabet_clist,
 alphabet .initial:n = { A, B, C, D, E, F, G, H, I, J, K, L, M,
 N, O, P, Q, R, S, T, U, V, W, X, Y, Z }
 }
% variables
\tl_new:N \l__vigenere_tablebody_tl
\seq_new:N \l__vigenere_alphabet_seq
% internal function
\cs_new_protected:Nn \vigenere_tabular:n
 {
 \group_begin:
 % set the keys
 \keys_set:nn { vigenere } { #1 }
 % make a sequence from the alphabet
 \seq_set_from_clist:NN \l__vigenere_alphabet_seq \l__vigenere_alphabet_clist
 % set the font and the tabcolsep
 \__vigenere_font:
 \dim_set_eq:NN \tabcolsep \l__vigenere_tabcolsep_dim
 % prepare the table body
 \tl_clear:N \l__vigenere_tablebody_tl
 \prg_replicate:nn { \seq_count:N \l__vigenere_alphabet_seq }
 {
 \tl_put_right:Nx \l__vigenere_tablebody_tl
 {
 \seq_use:Nn \l__vigenere_alphabet_seq { & }
 \exp_not:n { \\ \hline }
 }
 \seq_pop_left:NN \l__vigenere_alphabet_seq \l_tmpa_tl
 \seq_put_right:NV \l__vigenere_alphabet_seq \l_tmpa_tl
 }
 % make the table
 \tabular { | *{\clist_count:N \l__vigenere_alphabet_clist }{ c| } }
 \hline
 \tl_use:N \l__vigenere_tablebody_tl
 \endtabular
 \group_end:
 }
\ExplSyntaxOff
\begin{document}
\printvigeneretabular
\printvigeneretabular[font=\tiny,alphabet={1,2,3,4,5,6,7,8,9,10},tabcolsep=1pt]
\end{document}