Kdtyjb

Based on this question, I have created a simple macro that prints and stores its argument, and if it is issued again with the identical argument it prints nothing:

% !TEX TS-program = xelatexmk

RequirePackage{filecontents}



begin{filecontents}{mypackage.sty}

NeedsTeXFormat{LaTeX2e}

ProvidesPackage{mypackage}



newenvironment{myenv}{ignorespaces}{parignorespacesafterend}



DeclareOption{skiprepetitions}{%

  AtBeginDocument{letmypackage@printmypackage@print@skip}%

}

DeclareOption{keeprepetitions}{%

  AtBeginDocument{letmypackage@printmypackage@print@keep}%

}

ExecuteOptions{keeprepetitions}

ProcessOptionsrelax



RequirePackage{xifthen}



defmypackage@storedval{} % create a macro to later store a value in



newcommand{mycommand}[1]{%

  ifthenelse{isempty{#1}}

    {% if empty just print an empty line

     mbox{}%

    }

    {% if not empty

     mypackage@print{#1}%

     defmypackage@storedval{#1}%

    }%

}



defmypackage@print@skip#1{%

  ifthenelse{equal{#1}{mypackage@storedval}}

   {mbox{}}

   {#1}%

}

defmypackage@print@keep#1{#1\}



end{filecontents}



documentclass{article} 



usepackage[skiprepetitions]{mypackage}



begin{document}



begin{myenv}

mycommand{A} \ %A

mycommand{A} \  %empty

mycommand{A} \  %empty

mycommand{} \    %empty

mycommand{B} \  %B

mycommand{C} \  %C

mycommand{C} \  %empty

mycommand{A} \  %A

end{myenv}



begin{myenv}

mycommand{A} \ %A  

mycommand{A} \ %empty



newpage



mycommand{A} \ %A 

end{myenv}



end{document}

I would like to now have it "reset" or "forget" what is stored at pagebreaks and boundaries of a specific environment, so that on a new page, or in a new environment it does print its argument even if the previous one was identical.

Outcommented in the document above are the values that I expect to see.

As far as I understood, the following does what you want (thanks to David Carlisle's comment for the hint about perpage!):

RequirePackage{filecontents}



begin{filecontents}{mypackage.sty}

NeedsTeXFormat{LaTeX2e}

ProvidesPackage{mypackage}



RequirePackage{perpage}



newcounter{mycounter}

MakePerPage{mycounter}



newenvironment{myenv}{%

  % mycommand is only defined inside the environment

  letmycommandmy@command

  % Make sure the next mycommand isn't ignored, even if its argument

  % matches the value stored in mypackage@storedval.

  setcounter{mycounter}{0}%

  ignorespaces

}{%

  parignorespacesafterend

}



DeclareOption{skiprepetitions}{%

  AtBeginDocument{letmypackage@printmypackage@print@skip}%

}

DeclareOption{keeprepetitions}{%

  AtBeginDocument{letmypackage@printmypackage@print@keep}%

}

ExecuteOptions{keeprepetitions}

ProcessOptionsrelax



RequirePackage{xifthen}



defmypackage@storedval{} % create a macro to later store a value in



newcommand{my@command}[1]{%

  ifthenelse{isempty{#1}}%

    {% if empty just print an empty line

     mbox{}%

    }%

    {% If this is the first stepcounter{mycounter} executed since the current

     % page was started, this sets 'mycounter' to 1.

     stepcounter{mycounter}%

     mypackage@print{#1}%

     defmypackage@storedval{#1}%

    }%

}



defmypackage@print@skip#1{%

  ifthenelse{cnttest{value{mycounter}}>{1}AND

              equal{#1}{mypackage@storedval}}%

   {mbox{}}%

   {#1}%

}

defmypackage@print@keep#1{#1\}



end{filecontents}



documentclass{article}



usepackage[skiprepetitions]{mypackage}



begin{document}

setlength{parindent}{0pt}



begin{myenv}

mycommand{A}\  %A

mycommand{A}\  %empty

mycommand{A}\  %empty

mycommand{}\   %empty

mycommand{B}\  %B

mycommand{C}\  %C

mycommand{C}\  %empty

mycommand{A}\  %A

end{myenv}



begin{myenv}

mycommand{A}\ %A

mycommand{A}\ %empty



newpage



mycommand{A}\ %A

end{myenv}



end{document}

I used a new counter called mycounter that is subject to MakePerPage{mycounter}. This implies that the first stepcounter{mycounter} on any given page resets mycounter to 1,^a because 1 is the default value of the optional argument of MakePerPage.

I made it so that at the beginning of myenv, mycounter is set to 0. Besides, stepcounter{mycounter} is executed whenever mycommand is called with a non-empty argument. Therefore, after this stepcounter{mycounter} is performed, mycounter is equal to 1 if and only if:

• this is the first mycommand call on the current page, or;




• this is the first mycommand call in the current myenv environment.

This is the basis for the “ignoring criterion” you need. The only other thing to check is that, when we are in “possibly-ignoring mode”,^b the argument passed to mycommand differs from the saved value (since all this comes after the emptyness check).

Note that I renamed your mycommand to my@command and do letmycommandmy@command only inside the myenv environment, so that if you have a call to mycommand that lies out of any myenv environment, LaTeX will report an error (undefined command).

You may want to move the stepcounter{mycounter} call at the beginning of the my@command macro: this depends on the behavior you want when an empty argument is passed. Should it make the new state be “possibly-ignoring mode”, or should it let the state unchanged (in my code: the latter)? This is a decision that belongs to you. But since you just output an mbox{} for empty arguments, the difference won't be very visible in general...

Footnotes

a. After two compilation runs, since the perpage package relies on the .aux file.

b. I.e., the argument is non-empty and the mycommand call is neither the first-on-page nor the first-in-environment.