Why does cleveref's \crefname command have no effect when it appears within a \foreach?

Question

This question follows on from this one, which I asked a few weeks ago. I have since discovered the cleveref package, and I would like to use it for ease in referring to theorem-like environments without having to remember whether a given statement was a theorem, a lemma, a proposition, etc.

Here is a small example document. When I compile this document, the final line of text begins "Here are some references to ?? 1.1, ?? 1.2 and theorem 1.3." The attempt to use \crefname to set reference names (I'm not up on the terminology) for the different environments is not working. However, if the line marked with % (*) is uncommented, the second "??" will become "toybox". So it is something to do with being in a \foreach. But I can't find a way to make it work. It is as though the invocation of \crefname is totally ignored within the \foreach. Why does this happen?

\documentclass[a4paper]{amsart}

\def\myTheoremEnvironments{%
    theorem/theorems,%
    cobblestone/cobblestones,%
    toybox/toyboxes%
}

\usepackage{tikz, titlecaps, cleveref}

% Number all definition, theorem, etc. environments using the same counter.
% Start counting again at the start of each section.
% Style these environments using LaTeX's "definition" style.
\theoremstyle{definition}
\newtheorem{baseTheorem}{Base Theorem}[section]
\foreach \x/\y in \myTheoremEnvironments {
    \edef\tmp{\noexpand\newtheorem{\x}[baseTheorem]{\noexpand\titlecap{\x}}}\tmp
    \crefname{\x}{\x}{\y}
}

%\crefname{toybox}{toybox}{toyboxes} % (*)

\begin{document}

\section{Hello, and welcome to my document.}

\begin{cobblestone}
    \label{csref}
    Hello. I am an ``cobblestone'' environment.
\end{cobblestone}

\begin{toybox}
    \label{tbref}
    I am a ``toybox'' environment. What a strange name that is for an environment.
\end{toybox}

\begin{theorem}
    \label{thmref}
    People trying to do strange things with ``foreach'' should expect trouble.
\end{theorem}

Here are some references to \cref{csref}, \cref{tbref} and \cref{thmref}.
I could have tried using just one call to ``cref'' here,
but it's best not to run before you can walk.

\end{document}

Answer 1

The big problem is that \foreach does each cycle inside a group; while \newtheorem definitions are global, \crefname definitions aren't.

I suggest a perhaps more user-friendly interface.

\documentclass[a4paper]{amsart}

\usepackage{titlecaps, cleveref}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\foreachpair}{smm}
 {
  \IfBooleanTF{#1}
   {
    \hammerite_foreachpair:on { #2 } { #3 }
   }
   {
    \hammerite_foreachpair:nn { #2 } { #3 }
   }
 }

\cs_new_protected:Npn \hammerite_foreachpair:nn #1 #2
 {
  \cs_set:Npn \__hammerite_temp:nn ##1 ##2 { #2 }
  \clist_map_inline:nn { #1 } { \__hammerite_dopair:n { ##1 } }
 }
\cs_new:Npn \__hammerite_dopair:n #1
 {
  \__hammerite_dopair:wn #1 \q_stop
 }
\cs_new:Npn \__hammerite_dopair:wn #1/#2 \q_stop
 {
  \__hammerite_temp:nn { #1 } { #2 }
 }
\cs_generate_variant:Nn \hammerite_foreachpair:nn { o }
\ExplSyntaxOff

% Number all definition, theorem, etc. environments using the same counter.
% Start counting again at the start of each section.
% Style these environments using LaTeX's "definition" style.

\theoremstyle{definition}

\newtheorem{baseTheorem}{Base Theorem}[section]

\foreachpair
 {
  theorem/theorems,
  cobblestone/cobblestones,
  toybox/toyboxes,
 }
 {
  \newtheorem{#1}[baseTheorem]{\titlecap{#1}}
  \crefname{#1}{#1}{#2}
 }

\begin{document}

\section{Hello, and welcome to my document.}

\begin{cobblestone}\label{csref}
Hello. I am an ``cobblestone'' environment.
\end{cobblestone}

\begin{toybox}\label{tbref}
I am a ``toybox'' environment. What a strange name that is for an environment.
\end{toybox}

\begin{theorem}\label{thmref}
People trying to do strange things with ``foreach'' should expect trouble.
\end{theorem}

Here are some references to \cref{csref}, \cref{tbref} and \cref{thmref}.
I could have tried using just one call to ``cref'' here,
but it's best not to run before you can walk.

\end{document}

As you see, the second argument of \foreachpair is a comma separated list of items of the form <item-a>/<item-b>; the second argument is like a command definition, at each cycle <item-a> is substituted for #1 and <item-b> is substituted for #2.

There's also an alternative way of calling it

\newcommand\myTheoremEnvironments{
  theorem/theorems,
  cobblestone/cobblestones,
  toybox/toyboxes
}

\foreachpair* \myTheoremEnvironments
 {
  \newtheorem{#1}[baseTheorem]{\titlecap{#1}}
  \crefname{#1}{#1}{#2}
 }

Answer 2

\foreach does each iteration in a group and furthermore \crefname does not expand its second argument.

One can circumvent these problems using \xintForpair from package xinttools:

\documentclass[a4paper]{amsart}


\usepackage{tikz, titlecaps, cleveref}

% Number all definition, theorem, etc. environments using the same counter.
% Start counting again at the start of each section.
% Style these environments using LaTeX's "definition" style.
\theoremstyle{definition}
\newtheorem{baseTheorem}{Base Theorem}[section]

% Does not work: 
% \def\myTheoremEnvironments{%
%     theorem/theorems,%
%     cobblestone/cobblestones,%
%     toybox/toyboxes%
% }
% \foreach \x/\y in \myTheoremEnvironments {
%     \edef\tmp{\noexpand\newtheorem{\x}[baseTheorem]{\noexpand\titlecap{\x}}}\tmp
%     \crefname{\x}{\x}{\y}
% }

% alternative using \xintForpair:

\usepackage{xinttools}% http://ctan.org/pkg/xint

\xintForpair #1#2 in 
{% spaces around commas or like the end of lines here, 
 % or around parentheses are removed automatically
   (theorem,theorems),
   (cobblestone,cobblestones),
   (toybox,toyboxes)
}
\do
{%  (spaces significant but do not matter)
    \newtheorem{#1}[baseTheorem]{\titlecap{#1}}
    \crefname{#1}{#1}{#2}
}

\begin{document}\thispagestyle{empty}

\section{Hello, and welcome to my document.}

\begin{cobblestone}
    \label{csref}
    Hello. I am an ``cobblestone'' environment.
\end{cobblestone}

\begin{toybox}
    \label{tbref}
    I am a ``toybox'' environment. What a strange name that is for an environment.
\end{toybox}

\begin{theorem}
    \label{thmref}
    People trying to do strange things with ``foreach'' should expect trouble.
\end{theorem}

Here are some references to \cref{csref}, \cref{tbref} and \cref{thmref}.
I could have tried using just one call to ``cref'' here,
but it's best not to run before you can walk.

\end{document}

Answer 3

[Y]ou can […] use the .list handler that uses \foreach internally but

• doesn’t group its content […] and
• can be used with the already expanded content as #1 (rather than as a macro sequence).

Using

\pgfkeys{/utils/my Foreach/.code args={#1/#2}{\newtheorem{#1}[baseTheorem]{\titlecap{#1}}%
                                              \crefname{#1}{#1}{#2}},
         /utils/my Foreach/.list/.expand once=\myTheoremEnvironments}

gives