2

If one defines a command with a key-value argument, say \ket[<key=value>]{<stuff>}, one gets the wrong output when nesting it (in my opinion). E.g. \ket[delim = |)]{ \ket{\psi} } changes the delimiters of both kets, but should only do it for the outer one, if \ket is defined as

\NewDocumentCommand{\ket}{ o m }
{
\group_begin:
    \IfNoValueF{#1} { \mymodule_set_keys:n {#1} }
    \mymodule_ket:n {#2}
\group_end:
}

A quick solution would be to set the keys to their default values when the o-argument is not given as below.

\NewDocumentCommand{\ket}{ o m }
{
\group_begin:
    \IfNoValueTF{#1}
      { \mymodule_set_keys:n { delim } }
      { \mymodule_set_keys:n {#1} }
    \mymodule_ket:n {#2}
\group_end:
}

This solution wouldn't allow changes made by the user with \mymoduleset (I call this 'user default' in the MWE's comments below), say \mymoduleset[delim = \langle|].

The idea is that when the command \ket is defined, it should initially use the packages default values i.e. delim .default:n = {\lvert\rangle}, but when the user want a different output for all \ket's (globally in some sense), then he can change it with \mymoduleset, such that \ket{<stuff>} produces \langle <stuff> | when \mymoduleset[delim = \langle|] is used.

How can one achieve a solution, which

  • allows 'global' changes by the user with \mymoduleset
  • and local changes i.e. \ket[<key=value>]{<stuff>} doesn't affect inner \ket's when nestet i.g. \ket[delim = |)]{ \ket{\psi} }

MWE

\documentclass{article}
\usepackage{xparse}
\usepackage{amsmath}

\ExplSyntaxOn

\tl_new:N \l__mymodule_ket_delim_tl

\keys_define:nn { mymodule }
{
    delim .tl_set:N  = \l__mymodule_ket_delim_tl,
    delim .default:n = {\lvert\rangle}
}

\cs_new_protected:Npn \mymodule_ket:n #1
{
    \tl_item:Nn \l__mymodule_ket_delim_tl {1}
    #1
    \tl_item:Nn \l__mymodule_ket_delim_tl {2}
}

\cs_new_protected:Npn \mymodule_set_keys:n #1
{ \keys_set:nn { mymodule } {#1} }

\NewDocumentCommand{\ket}{ o m }
{
\group_begin:
    \IfNoValueTF{#1}
    { \mymodule_set_keys:n { delim } } % package default, but should be user default
    { \mymodule_set_keys:n {#1} }      % local change for this macro only

    \mymodule_ket:n {#2}
\group_end:
}

\NewDocumentCommand{\mymoduleset}{ o }
{
    \IfNoValueTF{#1}
    { \mymodule_set_keys:n { delim } } % Package default
    { \mymodule_set_keys:n {#1}      } % User default
}
\ExplSyntaxOff
\mymoduleset

\begin{document}
    \begin{align}
        \ket{\psi}                     &\quad \text{desired result: } | \psi \rangle \\
        \ket{ \ket{\psi} }             &\quad \text{desired result: } || \psi \rangle\rangle \\
        \ket[delim = |)]{ \ket{\psi} } &\quad \text{desired result: } || \psi \rangle ) \\
        \ket{ \ket[delim = |)]{\psi} } &\quad \text{desired result: } || \psi ) \rangle
    \end{align}

    \mymoduleset[delim = {\langle\rvert}]

    \begin{align}
        \ket{\psi}                     &\quad \text{desired result: } \langle \psi | \\
        \ket{ \ket{\psi} }             &\quad \text{desired result: } \langle\langle \psi || \\
        \ket[delim = (|]{ \ket{\psi} } &\quad \text{desired result: } ( \langle \psi || \\
        \ket{ \ket[delim = (|]{\psi} } &\quad \text{desired result: } \langle ( \psi ||
    \end{align}
\end{document}

enter image description here

Note: The MWE above is not the actual use case but illustrate the problem. The actual use case is too long to write here

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1
  • Beyond 'That's not how grouping works in TeX', I'm not sure what an answer here can be
    – Joseph Wright ♦
    Jan 27, 2020 at 21:10

2 Answers 2

Reset to default
4

You can use a meta key.

\documentclass{article}
\usepackage{xparse}
\usepackage{amsmath}

\ExplSyntaxOn

\tl_new:N \l__mymodule_ket_delim_tl

\keys_define:nn { mymodule }
 {
  delim   .tl_set:N = \l__mymodule_ket_delim_tl,
 }

\cs_new_protected:Npn \mymodule_ket:n #1
 {
  \tl_item:Nn \l__mymodule_ket_delim_tl {1}
  #1
  \tl_item:Nn \l__mymodule_ket_delim_tl {2}
 }

\cs_new_protected:Npn \mymodule_set_keys:n #1
 {
  \keys_set:nn { mymodule } {#1}
 }

\NewDocumentCommand{\ket}{ O{} m }
 {
  \group_begin:
  \mymodule_set_keys:n {default,#1} % local change for this macro only
  \mymodule_ket:n {#2}
  \group_end:
 }

\NewDocumentCommand{\mymoduleset}{m}
 {
  \keys_define:nn { mymodule }
   {
    default .meta:n = { #1 }
   }
 }

\ExplSyntaxOff

% initialize
\mymoduleset{delim=\lvert\rangle}

\begin{document}

\begin{align}
  \ket{\psi}                     &\quad \text{desired result: } | \psi \rangle \\
  \ket{ \ket{\psi} }             &\quad \text{desired result: } || \psi \rangle\rangle \\
  \ket[delim = |)]{ \ket{\psi} } &\quad \text{desired result: } || \psi \rangle ) \\
  \ket{ \ket[delim = |)]{\psi} } &\quad \text{desired result: } || \psi ) \rangle
\end{align}

\mymoduleset{delim = \langle\rvert}

\begin{align}
  \ket{\psi}                     &\quad \text{desired result: } \langle \psi | \\
  \ket{ \ket{\psi} }             &\quad \text{desired result: } \langle\langle \psi || \\
  \ket[delim = (|]{ \ket{\psi} } &\quad \text{desired result: } ( \langle \psi || \\
  \ket{ \ket[delim = (|]{\psi} } &\quad \text{desired result: } \langle ( \psi ||
\end{align}

\end{document}

enter image description here

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1
  • And here I thought you couldn't define keys that already existed (here default). Nice, shorter and less cumbersome solution than mine.
    – Simon
    Feb 1, 2020 at 20:30
2

As commented by Joseph, the solution I sought is beyond how grouping works in TeX. So I came up with a work-around solution, where I store the user default in a sequence, and it is used in \ket to set the keys to the user default. While I can't prevent 'local changes', i.e. \ket[<key=value>]{<stuff>}, from affecting inner kets, I can always use this sequence to override the local changes, so they effectively only apply to one command.

\documentclass{article}
\usepackage{xparse}
\usepackage{amsmath}

\ExplSyntaxOn

\tl_new:N \l__mymodule_ket_delim_tl
\seq_new:N \l__mymodule_user_default_seq

\seq_const_from_clist:Nn \l__mymodule_pkg_default_seq { delim }

\keys_define:nn { mymodule }
{
    delim .tl_set:N  = \l__mymodule_ket_delim_tl,
    delim .default:n = {\lvert\rangle}
}

\cs_new_protected:Npn \mymodule_ket:n #1
{
    \tl_item:Nn \l__mymodule_ket_delim_tl {1}
    #1
    \tl_item:Nn \l__mymodule_ket_delim_tl {2}
}

\cs_new_protected:Npn \mymodule_set_keys:n #1
{ \keys_set:nn { mymodule } {#1} }

\cs_new_protected:Npn \mymodule_new_ket:N #1
{
    \NewDocumentCommand{#1}{ o m }
    {
    \group_begin:
        % Use user default
        \exp_args:Nf \mymodule_set_keys:n { \seq_use:Nn \l__mymodule_user_default_seq {,} }
        \IfNoValueF{##1}
        {
            % local change
            \mymodule_set_keys:n {##1}
        }

        \mymodule_ket:n {##2}
    \group_end:
    }
}

\NewDocumentCommand{\NewKet}{ m o }
{
    \seq_set_eq:NN \l__mymodule_user_default_seq \l__mymodule_pkg_default_seq
    \IfNoValueTF{#2}
    {
        % Set to package default
        \mymodule_set_keys:n { delim }
    }
    {
        % Set to user default
        \mymodule_set_keys:n {#2}
        \seq_put_right:Nn \l__mymodule_user_default_seq {#2}
    }
    \mymodule_new_ket:N #1
}

\NewDocumentCommand{\mymoduleset}{ o }
{
    \IfNoValueTF{#1}
    {
        % Set to package default
        \mymodule_set_keys:n { delim }
        \seq_set_eq:NN \l__mymodule_user_default_seq \l__mymodule_pkg_default_seq
    }
    {
        % Set to user default
        \mymodule_set_keys:n {#1}
        \seq_put_right:Nn \l__mymodule_user_default_seq {#1}
    }
}

\ExplSyntaxOff

\NewKet{\ket}

\begin{document}
    \begin{align}
        \ket{\psi}                     &\quad \text{desired result: } | \psi \rangle \\
        \ket{ \ket{\psi} }             &\quad \text{desired result: } || \psi \rangle\rangle \\
        \ket[delim = |)]{ \ket{\psi} } &\quad \text{desired result: } || \psi \rangle ) \\
        \ket{ \ket[delim = |)]{\psi} } &\quad \text{desired result: } || \psi ) \rangle
    \end{align}

    \mymoduleset[delim = {\langle\rvert}]

    \begin{align}
        \ket{\psi}                     &\quad \text{desired result: } \langle \psi | \\
        \ket{ \ket{\psi} }             &\quad \text{desired result: } \langle\langle \psi || \\
        \ket[delim = (|]{ \ket{\psi} } &\quad \text{desired result: } ( \langle \psi || \\
        \ket{ \ket[delim = (|]{\psi} } &\quad \text{desired result: } \langle ( \psi ||
    \end{align}
\end{document}

This gives the desired result

enter image description here

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