How would you expand a macro twice in LaTeX 2 (or 2epsilon). I am aware of the question What is the preferred way of expanding twice in expl3?, but I'm curious as to how you'd do it in LaTeX.

I'd like to point out that I suspect that if you actually need to do this in your code, you'd probably want to reformulate your code and not find a way to do this. However, I'm still curious for educational purposes.

Below is my (failing) attempt

documentclass{article}

makeatletter

% Command for printing stuff to the error log

definspect#1{@latex@warning{string#1:meaning#1}}

makeatother

defa{3}

defb{2a}

defc{1b}

% I want to obtain a macro containing "12a" from using only c

% Expand once

edefexpandedOnce{unexpandedexpandafter{c}}

inspectexpandedOnce

%% ^ produces 1b in the error log

expandafterexpandafteredefexpandafterexpandedTwice{unexpandedexpandafter{expandedOnce}}

inspectexpandedTwice

%% ^ Also produces 1b in the error log, but I'd want it to

%% produce 12a

begin{document}

~

end{document}

I get

> zz=macro:

->12a 12a .

on the terminal from etex (or pdftex) from

defa{3}

defb{2a}

defc{1b1b}

defafterfi#1fi{fi#1}

deffoo#1{ifxrelax#1elseafterfiexpandafterunexpandedexpandafter{#1}foofi}

edefzz{expandafterfoocrelax}



showzz



bye

Note that this is the expansion order that you asked for, as far as I can tell but is not the order that TeX would use normally so it isnt really "expanding twice"

Consider

defa{b} defb#1{}  defc{zzzzz}

defz{ac}

by your definition I think you want to expand a and c once in the first step so getting a "first expansion" of z as b zzzzz then on a second step expand b so get zzzz.

However TeX would fully expand the first token at each stage, so in the first step get bc then in the second step get an empty list. c would never be expanded at all by TeX.

New answer

The following expands every token in tmp (which is what you want, I hope) in a more reliable way. I didn't test it thoroughly though.

documentclass{article}



newcommandfoo{bazA}

newcommandbazA{bazB}

newcommandbazB{bar}



defa{3}

defb{2a}

defc{1{b}}



defafterfi#1fi{fi#1}

makeatletter

defq@stop{q@stop}

defexpandingloop@a#1#%

  {%

    expandingloop@b#1q@stop

    expandingloop@c

  }

defexpandingloop@b#1%

  {%

    ifxq@stop#1%

    else

      afterfiunexpandedexpandafter{#1}expandingloop@b

    fi

  }

newcommandexpandingloop@c[1]

  {%

    ifxq@stop#1%

    else

      afterfi{expandingloop@a#1{q@stop}}expandingloop@a%

    fi

  }

newcommandsingleallexpand[1]

  {%

    edef#1{expandafterexpandingloop@a#1{q@stop}}%

  }

makeatother



newcommandMeaning[1]{texttt{meaning#1}}





begin{document}

noindent

For verb|foo|:



lettmpfoo

Unexpanded:

Meaningtmp



singleallexpandtmp

Expanded once:

Meaningtmp



singleallexpandtmp

Expanded twice:

Meaningtmp



noindent

For verb|c|:



lettmpc

Unexpanded:

Meaningtmp



singleallexpandtmp

Expanded once:

Meaningtmp



singleallexpandtmp

Expanded twice:

Meaningtmp

end{document}

Old answer

Both of the following only expand the first token.

You can use edeffooA{unexpandedexpandafterexpandafterexpandafter{fooB}} to define fooA to be the same as a fooB expanded twice.

Doing stuff with a temporary macro one could do something like the following.

documentclass{article}



newcommandfoo{bazA}

newcommandbazA{bazB}

newcommandbazB{bar}



newcommandsingleexpand[1]

  {%

    edef#1{unexpandedexpandafterexpandafterexpandafter{#1}}%

  }



newcommandMeaning[1]{texttt{meaning#1}}





begin{document}

lettmpfoo

Unexpanded:

Meaningtmp



singleexpandtmp

Expanded once:

Meaningtmp



singleexpandtmp

Expanded twice:

Meaningtmp

end{document}

Being evil when the argument contains a group (but it works in the minimal example, everything else is a matter of adding an infinite number of tests):

defafterfi#1fi{fi#1}

defexpandingloop#1#2endexpandingloop

  {%

    unexpandedexpandafter{#1}%

    ifrelaxdetokenize{#2}relax

    else

      afterfiexpandingloop#2endexpandingloop

    fi

  }

newcommandsingleallexpand[1]

  {%

    edef#1{expandafterexpandingloop#1endexpandingloop}%

  }