Is there something similar to \itshape but for \emph text?

Question

Edit: this question is misinformed and the chosen answer answers a different question altogether.

\emph produces slightly better italicized text for certain symbols, e.g., punctuation. Right now, I use \itshape to force a style on a block of text.

\lstdefinelanguage{Scheme}{
  % basewidth=0.5em,
  sensitive=true,
  basicstyle=\normalsize\rmfamily,
  commentstyle=\itshape\rmfamily\color[rgb]{.9, .5,.1},
  keywordstyle=\bfseries\sffamily\color[rgb]{0,.3,.7},
  morecomment=[l]{;},
  frameshape={RYR}{Y}{Y}{RYR},
  identifierstyle=\emph\rmfamily,
  keywords={define, lambda, let, cond, else},
  escapeinside={(*;}{;*)},
  columns=fullflexible
}

The problem is that I want to use \emph for "comments" in my listing and not just \itshape. Is there something similar that I can use (because I'd rather not have to escape and unescape every instance where I want to use \emph)?

Edit: it seems that \em is what I'm looking for, but my problem is more involved than that. The problem is that the identifierstyle doesn't italicize question marks using the above listing. See the image and code listing below.

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{listings, skins, breakable}
\definecolor{myorange}{rgb}{0.9, 0.5, 0.1}
\lstdefinelanguage{Scheme}{
  % basewidth=0.5em,
  sensitive=true,
  basicstyle=\normalsize\rmfamily,
  commentstyle=\itshape\rmfamily\color[rgb]{.9, .5,.1},
  keywordstyle=\bfseries\sffamily\color[rgb]{0,.3,.7},
  morecomment=[l]{;},
  frameshape={RYR}{Y}{Y}{RYR},
  identifierstyle=\em\rmfamily,
  keywords={define, lambda, let, cond, else},
  escapeinside={(;}{;)},
  columns=fullflexible
}
\begin{document}
\begin{lstlisting}[language=Scheme]
;; rember(;\textcolor{myorange}{\textrm{:}};) (;\textcolor{myorange}{\textsf{Atom}};) (;\textcolor{myorange}{\textsf{[ListOf Atom]}};) (;\textcolor{myorange}{$\to$};) (;\textcolor{myorange}{\textsf{Atom}};)
;;   Comment here...
(define rember
  ((;$\lambda$;) (a lat)
    (cond
      [(null? lat) (quote ())]
      [else (cond
              [(eqv? (car lat) a) (cdr lat)]
              [else (rember a (cdr lat))])])))
\end{lstlisting}
\end{document}

Answer 1

Unless you redefine \emph{}, by default it uses \em internally, that uses \itshape internally, so both commands should produce exactly the same italics:

\emph definition:

\ifmmode \nfss@text {\em #1}\else \hmode@bgroup \text@command {#1}\em \check@icl #1\check@icr \expandafter \egroup \fi

\em definition:

\@nomath \em \ifx \emfontdeclare@clist \@empty \ifdim \fontdimen \@ne \font >\z@ \eminnershape \else \itshape \fi \else \edef \em@currfont {\csname \curr@fontshape /\f@size \endcsname }\expandafter \do@emfont@update \emfontdeclare@clist \do@emfont@update \fi

The main difference, is that \emph, like \textit, corrects the space after the italics, while with \itshape or \em is your work make the so called "italic correction". That is, \emph{l}l or \textit{l}l will have some extra spacing between the two letters, compared with {\em l}l or {\itshape l}l, that are too close, and then is your work type {\em l\/}l or {\itshape l\/}l to avoid that.

Well, another important difference is that \emph or \em means "emphasis", not "italics", and therefore {\em l{\em l}l} will produce

while {\itshape l{\itshape l}l} will produce only italics, because it have sense emphasize a text in italics, but not italicize it again.

Therefore, is OK redefine \emph or better \em only if you to make emphasis with some that is not italics (e.g., bold or slant font) or return main font in nested emphasis, but you should avoid redefine \textit or\itshape because then the meaning of the commands are misleading and will produce unexpected results in any package using these commands.

As Mico warns in the comment, still one more difference is the math mode, fact that you can already suspect trying to decipher above the cryptic definitions, so you can type $\emph{x}$ or $\textit{x}$, but not ${\em x}$ nor ${\itshape x}}$.

Answer 2

The corresponding switch for \emph is \em.

So instead of \itshape you can use \em.

Answer 3

Listings will print the identifiers in italic, but the ? is not part of the identifiers.

You can force listings to print it in italic by making it a normal letter:

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{listings, skins, breakable}
\definecolor{myorange}{rgb}{0.9, 0.5, 0.1}
\lstdefinelanguage{Scheme}{
   basewidth=0.5em,
  sensitive=true,
  basicstyle=\normalsize\rmfamily,
  commentstyle=\itshape\rmfamily\color[rgb]{.9, .5,.1},
  keywordstyle=\bfseries\sffamily\color[rgb]{0,.3,.7},
  morecomment=[l]{;},
  frameshape={RYR}{Y}{Y}{RYR},
  identifierstyle=\itshape\rmfamily,
  alsoletter={?},
  keywords={define, lambda, let, cond, else},
  escapeinside={(;}{;)},
  columns=fullflexible
}
\begin{document}
\begin{lstlisting}[language=Scheme]
;; rember(;\textcolor{myorange}{\textrm{:}};) (;\textcolor{myorange}{\textsf{Atom}};) (;\textcolor{myorange}{\textsf{[ListOf Atom]}};) (;\textcolor{myorange}{$\to$};) (;\textcolor{myorange}{\textsf{Atom}};)
;;   Comment here...
(define rember
  ((;$\lambda$;) (a lat)
    (cond
      [(null? lat) (quote ())]
      [else (cond
              [(eqv? (car lat) a) (cdr lat)]
              [else (rember a (cdr lat))])])))
\end{lstlisting}
\itshape null?
\end{document}