Cfxtrjtrk

The following is actually a simplified version from a large job.

documentclass{memoir}



AtBeginDocument{First}



AtBeginDocument{Second}



AtBeginDocument{Third}



% I want to cancel the above at this point



AtBeginDocument{New First}



AtBeginDocument{New Second}



AtBeginDocument{New Third}



begin{document}



end{document}

I need to cancel the current AtBeginDocument accumulations at some midpoint (coming from another homegrown style file from which I need to use some of the macros) and then add some more.

How do I do this?

I'm not sure I understand your use case precisely. Left to myself, I'd be hugely reluctant to fiddle with AtBeginDocument (or @begindocumenthook) directly, because lots of packages (and the internal workings of LaTeX itself) use them for various purposes, and I don't see how I could be sure that I wouldn't break something unintentionally.

Might it be better to define a separate accumulator macro of your own, and then to have that executed AtBeginDocument? You can then safely mess with that macro to your heart's content, without clobbering anything else that has been innocently making use of AtBeginDocument.

Something like:

documentclass{memoir}



makeatletter

defMyAtBeginDocument{g@addto@macromy@begindocumenthook}

letmy@begindocumenthook@empty

defMyResetBeginDocument{globalletmy@begindocumenthook@empty}

AtBeginDocument{my@begindocumenthook}

makeatother



AtBeginDocument{THATpar}

MyAtBeginDocument{NOT THISpar}

MyResetBeginDocument

MyAtBeginDocument{THISpar}



begin{document}

We should see THIS then THAT!

end{document}

Note that THIS comes before THAT because my@begindocument is executed as part of @begindocumenthook before the additional material added by AtBeginDocument{THATpar} because it comes in via my@begindocumenthook which in turn got added to @begindocumenthook first. You might need to (and could) delay that addition until later.

AtBeginDocument just adds (appends) code to the 'hook' @begindocumenthook, at the beginning of the document the collected code is executed.

In theory you can clear the hook at any time with

makeatletter

let@begindocumenthook@empty

makeatother

but that might be a bit risky since many packages expect AtBeginDocument to work properly.

If there are only a few AtBeginDocuments you want to skip over, it might be safer to disable the command temporarily with

makeatletter

letAtBeginDocument@gobble

makeatother

Of course you can also save the contents of the hook

makeatletter

let@masroor@saved@begindocumenthook@begindocumenthook

makeatother

and then after a few AtBeginDocuments you want to ignore restore it again

makeatletter

let@begindocumenthook@masroor@saved@begindocumenthook

makeatother

This is similar to Paul Stanley's answer but with slightly different UI. This
defines AllowAtBeginDocumentToBeResetable which makes all subsequent uses of AtBeginDocument resetable. To reset these you invoke ClearResetableAtBeginDocumentList.
Thus your example code would look like:

AllowAtBeginDocumentToBeResetable%% ALL EXTERNAL PACKAGES INCLUDED BEFORE HERE



AtBeginDocument{Firstpar}

AtBeginDocument{Secondpar}

AtBeginDocument{Thirdpar}



ClearResetableAtBeginDocumentList% I want to cancel the above at this point



AtBeginDocument{New Firstpar}

AtBeginDocument{New Secondpar}

AtBeginDocument{New Thirdpar}

which produces:

Notes:

• Note that this requires that all external packages MUST be included before you issue AllowAtBeginDocumentToBeResetable.

Code:

documentclass{memoir}



makeatletter

    let@OldAtBeginDocumentAtBeginDocument

    newcommand{@ResetableBegindDoumentItems}{}%

    newcommand{AllowAtBeginDocumentToBeResetable}{%

        ifdefined@AtBeginDocumentIncludesResetableListelse

            gdef@AtBeginDocumentIncludesResetableList{}% Don't execute this again

            AtBeginDocument{@ResetableBegindDoumentItems}%

        fi

        renewcommand{AtBeginDocument}[1]{%

            g@addto@macro@ResetableBegindDoumentItems{{##1}}%

        }%

    }

    newcommand*{ClearResetableAtBeginDocumentList}{%

        gdef@ResetableBegindDoumentItems{}%

    }

makeatother





AllowAtBeginDocumentToBeResetable%% ALL EXTERNAL PACKAGES INCLUDED BEFORE HERE



AtBeginDocument{Firstpar}

AtBeginDocument{Secondpar}

AtBeginDocument{Thirdpar}



ClearResetableAtBeginDocumentList% I want to cancel the above at this point



AtBeginDocument{New Firstpar}

AtBeginDocument{New Secondpar}

AtBeginDocument{New Thirdpar}



begin{document}



end{document}

I can offer a few routines for introducing sub-hooks within the AtBeginDocument-hook and maintaining them.

1) AtBeginDocumentSubHook

Syntax:

AtBeginDocumentSubHook{⟨name of AtBeginDocument-sub-hook⟩}%

                       {⟨tokens⟩}%

Adds a new AtBeginDocument-sub-hook whose name is ⟨name of AtBeginDocument-sub-hook⟩ to the AtBeginDocument-hook and defines that AtBeginDocument-sub-hook to deliver ⟨tokens⟩.

2) AddToContentOfAtBeginDocumentSubHook

Syntax:

AddToContentOfAtBeginDocumentSubHook{⟨name of AtBeginDocument-sub-hook⟩}%

                                     {⟨prepend-tokens⟩}%

                                     {⟨append-tokens⟩}%

Redefines the AtBeginDocument-sub-hook whose name is ⟨name of AtBeginDocument-sub-hook⟩ to additionally deliver ⟨prepend-tokens⟩ in front of the tokens that are already in this sub-hook and to additionally deliver ⟨append-tokens⟩ behind the tokens that are already in this sub-hook.

3) ReplaceContentOfAtBeginDocumentSubHook

Syntax:

ReplaceContentOfAtBeginDocumentSubHook{⟨name of AtBeginDocument-sub-hook⟩}%

                                       {⟨tokens⟩}%

Redefines the AtBeginDocument-sub-hook whose name is ⟨name of AtBeginDocument-sub-hook⟩ to deliver ⟨tokens⟩.

4) RemoveAtBeginDocumentSubHook

Syntax:

RemoveAtBeginDocumentSubHook{⟨name of AtBeginDocument-sub-hook⟩}%

Removes the AtBeginDocument-sub-hook whose name is ⟨name of AtBeginDocument-sub-hook⟩ from the AtBeginDocument-hook.

documentclass{memoir}



makeatletter

%%----------------------------------------------------------------------

%% Paraphernalia

%%----------------------------------------------------------------------

newcommandUD@firstoftwo[2]{#1}%

newcommandUD@secondoftwo[2]{#2}%

newcommandUD@Exchange[2]{#2#1}%

newcommandUD@name{}longdefUD@name#1#{romannumeral0UD@innername{#1}}%

newcommandUD@innername[2]{%

  expandafterUD@Exchangeexpandafter{csname#2endcsname}{ #1}%

}%

%%----------------------------------------------------------------------

%% Check whether argument is empty:

%%......................................................................

%% UD@CheckWhetherNull{<Argument which is to be checked>}%

%%                     {<Tokens to be delivered in case that argument

%%                       which is to be checked is empty>}%

%%                     {<Tokens to be delivered in case that argument

%%                       which is to be checked is not empty>}%

%%

%% The gist of this macro comes from Robert R. Schneck's ifempty-macro:

%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>

newcommandUD@CheckWhetherNull[1]{%

  romannumeral0expandafterUD@secondoftwostring{expandafter

  UD@secondoftwoexpandafter{expandafter{string#1}expandafter

  UD@secondoftwostring}expandafterUD@firstoftwoexpandafter{expandafter

  UD@secondoftwostring}expandafterexpandafterUD@firstoftwo{ }{}%

  UD@secondoftwo}{expandafterexpandafterUD@firstoftwo{ }{}UD@firstoftwo}%

}%

%%----------------------------------------------------------------------

%% Remove AtBeginDocument-sub-hook from AtBeginDocument-hook:

%%......................................................................

%%  RemoveAtBeginDocumentSubHook{<name of AtBeginDocument-sub-hook>}

%%  removes the AtBeginDocument-sub-hook whose name is

%%  <name of AtBeginDocument-sub-hook> from the AtBeginDocument-hook.

newcommand*RemoveAtBeginDocumentSubHook[1]{%

   begingroup

   UD@namelongdefkeep##1{@begindocumentsubhook@#1}{##1}%

   UD@namelongdefremove##1{@begindocumentsubhook@#1}{}%

   expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

   expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

   expandafter

   UD@CheckWhetherNull

   expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

   expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

   expandafter

   {UD@nameexpandafterremove@begindocumenthook{@begindocumentsubhook@#1}}%

   {%

     endgroup

     @latex@info{Removal of undefined stringAtBeginDocument-sub-hookMessageBreak`#1' obsolete}%

   }{%

      @latex@info{Removing stringAtBeginDocument-sub-hookMessageBreak`#1'}%

      expandafterUD@Exchangeexpandafter{%

        expandaftertoks@expandafter{thetoks@}%

      }{%

        expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

        endgroup

        expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

        toks@

        expandafterexpandafterexpandafterexpandafterexpandafterexpandafterexpandafter

        {expandafterexpandafterexpandafter@gobbleexpandafterkeepexpandafter.@begindocumenthook}%

        xdef@begindocumenthook{thetoks@}%

      }%

   }%

   UD@namegloballet{@begindocumentsubhook@#1}=UndEFineD

}%

%%----------------------------------------------------------------------

%% Introduce new AtBeginDocument-sub-hook:

%%......................................................................

%%  AtBeginDocumentSubHook{<name of AtBeginDocument-sub-hook>}%

%%                         {<tokens>}%

%%  Adds a new AtBeginDocument-sub-hook whose name is

%%  <name of AtBeginDocument-sub-hook> to the AtBeginDocument-hook

%%  and defines that AtBeginDocument-sub-hook to deliver <tokens>.

newcommandAtBeginDocumentSubHook[2]{%

  @ifundefined{@begindocumentsubhook@#1}{%

    @latex@info{Introducing stringAtBeginDocument-sub-hookMessageBreak`#1'}%

    UD@namenewcommand{@begindocumentsubhook@#1}{}%

    expandafterUD@Exchangeexpandafter{%

      expandaftertoks@expandafter{thetoks@}%

      UD@nameAtBeginDocument{@begindocumentsubhook@#1}%

    }{%

      toks@{#2}%

      UD@namexdef{@begindocumentsubhook@#1}{thetoks@}%

    }%

  }{%

    @latex@error{Sub-Hook `#1' already definedon@line}{%

      Use either stringRemoveAtBeginDocumentSubHookspace for removing the sub-hook,MessageBreak

      or stringReplaceContentOfAtBeginDocumentSubHookspace for replacing the content of theMessageBreak

      sub-hook,MessageBreak

      or stringAddToContentOfAtBeginDocumentSubHookspace for adding tokens to the sub-hook.%

    }%

  }%

}%

%%----------------------------------------------------------------------

%% Replace all tokens of an AtBeginDocument-sub-hook:

%%......................................................................

%%  ReplaceContentOfAtBeginDocumentSubHook{<name of AtBeginDocument-sub-hook>}%

%%                                         {<tokens>}%

%%  Redefines the AtBeginDocument-sub-hook whose name is

%%  <name of AtBeginDocument-sub-hook> to deliver <tokens>.

newcommandReplaceContentOfAtBeginDocumentSubHook[2]{%

  @ifundefined{@begindocumentsubhook@#1}{%

    @latex@info{To be replaced stringAtBeginDocument-sub-hookMessageBreak`#1' does not exist}%

    AtBeginDocumentSubHook{#1}{#2}%

  }{%

    @latex@info{Replacing stringAtBeginDocument-sub-hookMessageBreak`#1'}%

    expandafterUD@Exchangeexpandafter{%

      expandaftertoks@expandafter{thetoks@}%

    }{%

      toks@{#2}%

      UD@namexdef{@begindocumentsubhook@#1}{thetoks@}%

    }%

  }%

}%

%%----------------------------------------------------------------------

%% Add tokens to an AtBeginDocument-sub-hook:

%%......................................................................

%%  AddToContentOfAtBeginDocumentSubHook{<name of AtBeginDocument-sub-hook>}%

%%                                       {<prepend-tokens>}%

%%                                       {<append-tokens>}%

%%  Redefines the AtBeginDocument-sub-hook whose name is

%%  <name of AtBeginDocument-sub-hook> to additionally deliver <prepend-tokens>

%%  in front of the tokens that are already in this hook and to additionally

%%  deliver <append-tokens> behind the tokens that are already in this hook.

newcommandAddToContentOfAtBeginDocumentSubHook[3]{%

  @ifundefined{@begindocumentsubhook@#1}{%

    @latex@info{stringAtBeginDocument-sub-hook `#1' where tokensMessageBreak shall be added does not exist}%

    AtBeginDocumentSubHook{#1}{#2#3}%

  }{%

    @latex@info{Adding tokens to stringAtBeginDocument-sub-hookMessageBreak`#1'}%

    expandafterUD@Exchangeexpandafter{%

      expandaftertoks@expandafter{thetoks@}%

    }{%

      toks@{#2}%

      toks@expandafterexpandafterexpandafter

            expandafterexpandafterexpandafterexpandafter{%

        UD@nametheexpandaftertoks@{@begindocumentsubhook@#1}#3%

      }%

      UD@namexdef{@begindocumentsubhook@#1}{thetoks@}%

    }%

  }%

}%

AtBeginDocument{%

  renewcommandRemoveAtBeginDocumentSubHook[1]{%

    @bsphack

    UD@namegloballet{@begindocumentsubhook@#1}=UndEFineD

    @latex@info{Removal of stringAtBeginDocument-sub-hook `#1'MessageBreak obsolete as not in preamble any more}%

    @esphack

  }%

  renewcommandAtBeginDocumentSubHook[2]{%

    @bsphack

    @latex@info{Introducing stringAtBeginDocument-sub-hook `#1'MessageBreak obsolete as not in preamble any more}%

    @esphack

    #2%

  }%

  renewcommandReplaceContentOfAtBeginDocumentSubHook[2]{%

    @bsphack

    @latex@info{Replacing stringAtBeginDocument-sub-hook `#1'MessageBreak obsolete as not in preamble any more}%

    @esphack

    #2%

  }%

  renewcommandAddToContentOfAtBeginDocumentSubHook[3]{%

    @bsphack

    @latex@info{Adding to stringAtBeginDocument-sub-hook `#1'MessageBreak obsolete as not in preamble any more}%

    @esphack

    #2#3%

  }%

}%

makeatother



%expandaftershowcsname @begindocumenthookendcsname



AtBeginDocumentSubHook{SomeSubHook}{Somepar}



AtBeginDocumentSubHook{FirstSubHook}{Firstpar}



AtBeginDocumentSubHook{SecondSubHook}{Secondpar}



AtBeginDocumentSubHook{ThirdSubHook}{Thirdpar}



AtBeginDocumentSubHook{FourthSubHook}{Fourthpar}



% Let's cancel/change some of the above at this point



RemoveAtBeginDocumentSubHook{SomeSubHook}



ReplaceContentOfAtBeginDocumentSubHook{FirstSubHook}{New Firstpar}



ReplaceContentOfAtBeginDocumentSubHook{SecondSubHook}{New Secondpar}



ReplaceContentOfAtBeginDocumentSubHook{ThirdSubHook}{Thi}



AddToContentOfAtBeginDocumentSubHook{ThirdSubHook}{New }{rdpar}



%expandaftershowcsname @begindocumenthookendcsname



begin{document}



end{document}