Environment with breakable text

Question

In the following code, I would like to use

\begin{tiScreen}
12345678901 234567890123456789

12345678901234567890123456789
\end{tiScreen}

instead of

\begin{tiScreen}
\breakabletexttt{12345678901} \breakabletexttt{234567890123456789}

\breakabletexttt{12345678901234567890123456789}
\end{tiScreen}

I also need to keep spaces using LaTeX convention : consecutive spaces are displayed as one.

The code

\documentclass{article}
    \usepackage{mdframed}

    \newenvironment{tiScreen}{%
        \ttfamily \begin{minipage}{9.5em}%
        \begin{mdframed}[innerrightmargin=0.2cm, innerleftmargin=0.2cm]%
    }{\end{mdframed} \end{minipage}}

    \makeatletter
        \newcommand\breakabletexttt{%
            \begingroup
                \catcode`\_=12 \catcode`\#=12
                \@breakabletexttt
        }
        \newcommand\@breakabletexttt[1]{%
                \ttfamily
                \breakable@texttt#1\@nil%
            \endgroup%
        }
        \def\@gobble@fi#1\fi{\fi#1}
        \def\breakable@texttt#1#2\@nil{%
            #1\hspace{0pt plus 0.1pt minus 0.1pt}%
            \ifx\relax#2\relax
            \else
                \@gobble@fi\breakable@texttt#2\@nil
            \fi
        }
    \makeatother


\begin{document}

    \breakabletexttt{12345678901 234567890123456789}

    \breakabletexttt{12345678901} \breakabletexttt{234567890123456789}

    \breakabletexttt{12345678901234567890123456789}

\end{document}

Answer 1

Here's a solution modelled on unbonpetit's one, which respect spaces and also newlines:

\documentclass{article}

\makeatletter
\newsavebox{\tiScreenbox}
\newenvironment{tiScreen}
  {\begin{lrbox}{\tiScreenbox}\ttfamily\minipage{9em}
   \catcode`\_=12 \catcode`\#=12 \obeyspaces \obeylines
   \begingroup\lccode`~=` \lowercase{\endgroup\def~}{\unskip\space}%
   \begingroup\lccode`~=` \lowercase{\endgroup\let\brt@space~}%
   \begingroup\lccode`~=`\^^M \lowercase{\endgroup\def~}{\ifvmode\else\endgraf\fi}%
   \breakabletexttt@i}
  {\vspace{-\baselineskip}\endminipage\end{lrbox}\fbox{\usebox\tiScreenbox}}

\long\def\breakabletexttt@i#1{%
  \ifx#1\end
    \expandafter\breakabletexttt@ii
  \else
    \ifx#1\brt@space
      \unskip\space
    \else
      #1\hskip\z@ plus.2em
    \fi
    \expandafter\breakabletexttt@i
  \fi}

\def\breakabletexttt@ii#1{%
    \end{#1}%
    \def\temp@{#1}\def\temp@@{tiScreen}%
    \ifx\temp@\temp@@\else
        \expandafter\breakabletexttt@i
    \fi}
\makeatother
\begin{document}
\begin{tiScreen}
1234567890123  4567890123456789

12345678901234567890123456789
\end{tiScreen}
\begin{tiScreen}
1234567890123  4567890123456789
123
12345678901234567890123456789
\end{tiScreen}
\end{document}

It has the advantage of not producing overfull and underfull boxes.

Answer 2

\documentclass{article}
\usepackage{mdframed}

\makeatletter
\newenvironment{tiScreen}
    {\ttfamily\minipage{9.5em}%
    \mdframed[innerrightmargin=0.2cm, innerleftmargin=0.2cm]%
    \catcode`\_=12 \catcode`\#=12 \breakabletexttt@i}
    {\endmdframed\endminipage}

\long\def\breakabletexttt@i#1{%
    \ifx#1\end
        \expandafter\breakabletexttt@ii
    \else
        #1\hskip\z@ plus.1pt minus.1pt
        \expandafter\breakabletexttt@i
    \fi}

\def\breakabletexttt@ii#1{%
    \end{#1}%
    \def\temp@{#1}\def\temp@@{tiScreen}%
    \ifx\temp@\temp@@\else
        \expandafter\breakabletexttt@i
    \fi}
\makeatother
\begin{document}
\begin{tiScreen}
12345678901234567890123456789

12345678901234567890123456789
\end{tiScreen}
\end{document}

if youy could describe what tokens can appear in your tiScreen environment, it would be easier to give a good aswer. This code takes spaces into account:

\documentclass{article}
\usepackage{mdframed}

\makeatletter
\newenvironment{tiScreen}
    {\ttfamily\parindent\z@\minipage{9.5em}%
    \mdframed[innerrightmargin=0.2cm, innerleftmargin=0.2cm]%
    \catcode`\_=12 \catcode`\#=12 \let\temp@@\@currenvir
    \testspc@}
    {\endmdframed\endminipage}

\def\testspc@{\futurelet\nxt@toks\testspc@i}

\def\testspc@i{%
    \ifx\nxt@toks\@sptoken\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi
    {\afterassignment\testspc@\let\nxt@toks= }\breakabletexttt@i}

\def\breakabletexttt@i{\afterassignment\breakabletexttt@ii\let\nxt@toks= }

\def\breakabletexttt@ii{%
    \ifx\nxt@toks\end
        \expandafter\breakabletexttt@iii
    \else
        \nxt@toks\hskip\z@ plus.1pt minus.1pt
        \expandafter\breakabletexttt@i
    \fi}

\def\breakabletexttt@iii#1{%
    \end{#1}\def\temp@{#1}%
    \unless\ifx\temp@\temp@@\expandafter\breakabletexttt@i\fi}
\makeatother
\begin{document}
\begin{tiScreen}
123456789012 34567890123456789

12345678901234567890123456789
\end{tiScreen}
\end{document}