Cfrtjryk

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?

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

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.

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}