Smalltalk language for listings.sty with specific literate chevron for the method pattern. Not that useful in practice, unless all listings are single methods…

lstsmalltalk.sty

\ProvidesFile{lstsmalltalk.sty}
    [2016/02/12 0.3 listings Smalltalk definitions file]
%
\RequirePackage{listings}
\RequirePackage{relsize}
\RequirePackage{calc}

\newcommand\language@smalltalk{smalltalk}

% all this needed to incept the above macro as the name of the language
% definition
\expandafter\expandafter\expandafter\lstdefinelanguage
\expandafter{\language@smalltalk}
{
  keywords={self,super,true,false,nil,thisContext},
  otherkeywords={^,:=,->,==,~=},
  alsoletter={\#:},
  string=[d]',
  comment=[s]{"}{"},
  literate={\ >>\ }{{\smalltalk@chevron}}3,
}[keywords,comments,strings]

\newif\ifsmalltalk@methodpattern
\smalltalk@methodpatterntrue

\lst@AddToHook{EndGroup}{% first line is class >> selector
    \global\smalltalk@methodpatterntrue}
\lst@AddToHook{EOL}{% switch >> back to operator appearance
    \global\smalltalk@methodpatternfalse}

\newcommand\smalltalk@methodpattern@chevron{\makebox[\widthof{>>>}][c]{\textsmaller{>>}}}
\newcommand\smalltalk@operator@chevron{>>}
\newcommand\smalltalk@chevron{%
  \ifsmalltalk@methodpattern
    \smalltalk@methodpattern@chevron
  \else
    \smalltalk@operator@chevron
  \fi}

\endinput
%%%
%%% And now for something completely different... Some stupid example,
%%% to put in a file to test this language definition...
%%%
% \lstset{
%   inputencoding=utf8,
%   columns=fullflexible,
%   basicstyle=\Large
% }
% 
% \begin{lstlisting}[language=Smalltalk]
% SomeClass >> testNumberOfRelationships
%   "this is a test"
%   | bazEntity |
%   self assert: fooEntity numberOfOutgoingRelationships = 1.
%   bazEntity := MyEntity named: #baz.
%   MyRelationship from: fooEntity to: bazEntity.
%   self assert: fooEntity numberOfOutgoingRelationships = 2.
%   string := 'Hello, world!'
%   aCollection do: [ each |
%     | local |
%     each someMessage ].
%   ^ string
% \end{lstlisting}
%%%%%%%%
% Local Variables:
% coding: utf-8
% End: