Boxes in the diagrams package

Question

I am trying to draw something like this using Paul Taylor's diagrams package

I've tried e.g.

\documentclass{article}
\usepackage{diagrams}
\begin{document}
\begin{diagram}
\mathrm{input} & \rTo & {\fbox{{\fbox{f}} \rTo {\fbox{g}}} & \rTo & \mathrm{output} \
\end{diagram}
\end{document}

But get

! Commutative Diagram: "*&" inserted between horizontal maps.
\cd@error ...pandafter \errmessage {\cd@name : #1}
l.839 ...\rTo & {\fbox{{\fbox{f}} \rTo {\fbox{g}}}
                                                   & \rTo & \mathrm{output} \

Is this even possible using diagrams?

EDIT:

The answer below answers the question I asked thank you very much.

I have a problem though - I am using a preprocessor to produce the TeX and this is interpreting |whatever| so I get

Is there any way of not using |...|? The preprocessor I am using is called lhs2tex and I couldn't see anything in its documentation on how to use something different.

What is your minimal working example, please? I see only a fragment. — Sebastiano, Apr 07 '23 at 12:03
https://tex.stackexchange.com/users/117876/sebastiano: that is my minimal working example but maybe you want me to add \begin{document} and \end{document}? I will do so — idontgetoutmuch, Apr 08 '23 at 14:23
Are you open to using TikZ-CD or just plain TikZ? I can't even get the manual's first example to run without errors. — Qrrbrbirlbel, Apr 08 '23 at 14:47
I am using Paul Taylor's diagrams package but I have found an answer that shows how to do it using tikz. — idontgetoutmuch, Apr 08 '23 at 14:50
https://tex.stackexchange.com/questions/48629/tikz-pgf-package-to-generate-flow-diagrams does what I want. — idontgetoutmuch, Apr 08 '23 at 14:51

score 3 · Accepted Answer · answered Apr 08 '23 at 16:18

I recommend TikZ-CD (or plain TikZ) with a few custom styles and keys to make life a bit easier.

Code

\documentclass{article}
\usepackage{tikz-cd}
\usetikzlibrary{bending} % for flex
\tikzcdset{
  boxes/.style={
    column sep=+1.3em,
    arrows={->,>={Triangle[angle'=45]}},
    every matrix/.append style={draw, inner sep=+.5em},
    cells={nodes={draw, minimum width=1cm, font=\mathstrut}}},
  io/.style args={#1:#2}{
    /tikz/column #1/.append style={nodes=input},
    /tikz/column #2/.append style={nodes=output}},
  diagrams={baseline=-axis_height},% https://tex.stackexchange.com/a/678935/16595
  @inputoutput/.style n args={5}{
    start anchor={#1},#2, to path={--+(#5:1.5em)\tikztonodes},
    execute at begin to=\tikzset{edge node={node[commutative diagrams/every cell,
      at end, anchor={#3}]{#4}}}},
  input/.style ={@inputoutput={west}{<-}{east}{input} {left}},
  output/.style={@inputoutput={east}{->}{west}{output}{right}}}
\tikzset{
  arrows={[quick]}, % bending only when we need it
  circ/.style={shape=circle, minimum size=+0pt},
  c/.style={shape=coordinate},
  @inputoutput/.style n args={4}{
    /utils/exec=\ar[{#1,#4}], append after command=(\tikzlastnode.#2)+(#3:.12cm)},
  input/.style={@inputoutput={input}{west}{left}{#1}},
  output/.style={@inputoutput={output}{east}{right}{#1}},
  shift down/.style={
    yshift=-\pgfkeysvalueof{/tikz/commutative diagrams/shift left/.@def}}}
\begin{document}
\begin{tikzcd}[boxes, io=1:1]
  |[circ]| f
\end{tikzcd}
\begin{tikzcd}[boxes, io=1:2]
   f \rar &  g
\end{tikzcd}
\bigskip
\begin{tikzcd}[boxes, row sep=2pt, io=1:2]
                                                      & f \
  |[c]| \urar[end anchor=west] \drar[end anchor=west] &   \
                                                      & g
\end{tikzcd}
\begin{tikzcd}[boxes, row sep=1em]
  |[input=shift right, output=shift left]| f \
  |[c]| \uar[-, out=  0, in= -5, end anchor={[shift down]east}, out looseness=2.2]
        \uar[   out=180, in=185, end anchor={[shift down]west}, out looseness=2.2,
             /tikz/arrows={[flex]}]
\end{tikzcd}
\end{document}

Output

See my comment on the preprocessor I am using. I can't find in the tikz documentation what |...| means — idontgetoutmuch, Apr 08 '23 at 17:36
@idontgetoutmuch | is just matrix of (math) nodes' way to escape to node options inside a cell. — Qrrbrbirlbel, Apr 08 '23 at 17:59

Boxes in the diagrams package

1 Answers1

Code

Output