How to compare an argument to a given string, within a 'newenvironment' definition?

Question

Problem description

I am trying to create an environment that produces boxed paragraphs with different styles.

So I tried to implement some "if"-"elif"-"else" blocks, that will compare the arguments passed to the environment to some given keywords to decide which style will be applied to a paragraph.

Unfortunately, implementing such an idea was far from being as simple as it sounds, since all the methods I tried (here), in order to compare an argument with a string did not give correct results.

MWE

Here is what I have tried (I got my inspiration from here):

\documentclass{article}
\usepackage{xcolor}
\usepackage[most]{tcolorbox}
\usepackage{ifthen}
%#################################
\newtcolorbox{mybox}[2][]{colback=black!5!white,colframe=black!45!white,fonttitle=\bfseries,enhanced,breakable,attach boxed title to top left={yshift*=-\tcboxedtitleheight/2},title={#2}}
%#################################
\makeatletter
\newcommand*\BEGININGcommands{}
\newcommand*\ENDINGcommands{}

\newenvironment{myENV}[1][]
{%
    \ifthenelse{\equal{#1}{keyword}}
    {
      % if '#1' == 'keyword' then apply the 'mybox' style to the selected paragraph
      \textcolor{green!35!white}{
      \textbf{Seeing this means that:} \fbox{\#1} and \fbox{keyword} represent the same string, which means that the content will be formatted by surrounding it with \textbf{mybox}.}\par\vspace{1em}
      \def\BEGININGcommands{\begin{mybox}[#1]}
      \def\ENDINGcommands{\end{mybox}}
    }
    {
      % else dont apply anything
      \textcolor{red!35!white}{\textbf{Seeing this means that:} \fbox{\#1} is not the same as \fbox{keyword}, which means that no formating will be applied.}\par\vspace{1em}
      \def\BEGININGcommands{}
      \def\ENDINGcommands{}
    }
    \BEGININGcommands
}
{%
    \ENDINGcommands%
}
\makeatother
%#################################
\begin{document}
\begin{myENV}{keywordA}
  This paragraph \textbf{should be formatted} as the \textbf{keywordA} is \textbf{specified}.
\end{myENV}
\par\vspace{2em}\noindent\rule{\textwidth}{1pt}\vspace{2em}
\begin{myENV}{keywordB}
  This paragraph \textbf{should not be formatted} as the \textbf{keywordA} is \textbf{not specified}.
\end{myENV}
\end{document}

Output

Desired output

Answer 1

You're using the wrong type and number of arguments.

For more than one choice, \ifthenelse becomes very cumbersome. I propose an expl3 solution with which it's easy to accommodate any number of choices for the keywords.

\documentclass{article}
\usepackage{xcolor}
\usepackage[most]{tcolorbox}

\newtcolorbox{myboxA}[1]{
  colback=black!5!white,
  colframe=black!45!white,
  fonttitle=\bfseries,
  enhanced,
  breakable,
  attach boxed title to top left={yshift*=-\tcboxedtitleheight/2},
  title={#1}
}
\newtcolorbox{myboxB}[1]{
  colback=red!5!white,
  colframe=red!45!white,
  fonttitle=\bfseries,
  enhanced,
  breakable,
  attach boxed title to top left={yshift*=-\tcboxedtitleheight/2},
  title={#1}
}

\ExplSyntaxOn

\NewDocumentEnvironment{myENV}{O{}}
 {
  \str_case:nn { #1 }
   {
    {keywordA}{\begin{myboxA}{#1}}
    {keywordB}{\begin{myboxB}{#1}}
   }
 }
 {
  \str_case:nn { #1 }
   {
    {keywordA}{\end{myboxA}}
    {keywordB}{\end{myboxB}}
   }
 }

\ExplSyntaxOff

\begin{document}

\begin{myENV}[keywordA]
  This paragraph \textbf{should be formatted} as the \textbf{keywordA} is \textbf{specified}.
\end{myENV}

\begin{myENV}[keywordB]
  This paragraph \textbf{should be formatted} as the \textbf{keywordB} is \textbf{specified}.
\end{myENV}

\begin{myENV}[foo]
  No formatting here.
\end{myENV}

\end{document}

Answer 2

Instead of creating separate tcolorbox environments for each possibility, create a style. Each style holds the key-value options associated with the formatting, that you can then pass via environment options.

\documentclass{article}

\usepackage{xcolor}
\usepackage[most]{tcolorbox}

\tcbset{
  % Define base style common to all boxes
  base/.style = {
    fonttitle = \bfseries,
    enhanced,
    breakable,
    attach boxed title to top left={yshift*=-\tcboxedtitleheight/2}
  },
  % Define keywordA-specific box style additions/overrides
  keywordA/.style = {
    colback = black!5!white,
    colframe = black!45!white,
  },
  % Define keywordB-specific box style additions/overrides
  keywordB/.style = {
    colback = red!5!white,
    colframe = red!45!white
  }
}

\NewDocumentEnvironment{myENV}{ O{} m }{%
  \begin{tcolorbox}[
    base, % load base style
    #1, % load additional style based on optional argument
    title = {#2} % Title in second (mandatory) argument
  ]
}{%
  \end{tcolorbox}
}

\begin{document}

\begin{myENV}[keywordA]{Something A}
  This paragraph \textbf{should be formatted} as the \textbf{keywordA} is \textbf{specified}.
\end{myENV}

\begin{myENV}[keywordB]{Something B}
  This paragraph \textbf{should be formatted} as the \textbf{keywordB} is \textbf{specified}.
\end{myENV}

\end{document}