Sstrhsrtj

I am creating a schedule for weekly lectures using the following code

documentclass{article}

usepackage{advdate}



%... Set the first lecture date

ThisYear{2019}

ThisMonth{3}

ThisDay{1}



newififfirst

    firsttrue

newcommand{nextlec}{%

  iffirst

    firstfalse

  else

    AdvanceDate[7]%

  fi

  section*{today}

}



begin{document}

nextlec

Lecture 01.



nextlec

Lecture 02.



nextlec

Lecture 03.



nextlec

Lecture 04.



nextlec

Lecture 05.



end{document}

The code works fine. Now, let's suppose there are holidays on March 08, March 29, April 18, May 17, and June 18.

My question is: how to redefine the nextlec to skip a holiday and return the next non-holiday date?

Note: this is not a duplicate from here, since I want to compare a calculated date to a set of several dates that I want to define.

EDITS:

After Jeffrey J Weimer suggestion (see comments), I tried to implemente the following piece code in my original one, but got a lot of error.

defholidays#1{def@holidays{#1}}

    newcommand{theholidays}{ {@holidays} }



newififfirst

    firsttrue



newcommand{jumpweek}{%

  iffirst

    firstfalse

  else

    AdvanceDate[7]%

  fi

}



newcommandnextlecbool{true}



newcommand{nextlec}{%

  jumpweek

  foeach holiday in theholidays

    while{nextlecbool}

      ifnum (10000*theyear + 100*themonth + theday) = holiday

        section*{today}

        Feriado.

        jumpweek

      else

        renewcommand{nextlecbool}{false}

      fi

    EndWhile

    ;

  renewcommand{nextlecbool}{true}

}

Perhaps this exhibits some tricks about recursive iteration and about using delimited arguments for taking apart strings of pattern

<word for month><space><number of day>,<space><year>

documentclass{article}

usepackage{datenumber}

usepackage{advdate}



makeatletter

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

% Section: Code for comparing dates.

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

% monthtonumber{<name of a month>} yields the number of that

% month (range 1..12; January -> 1, February -> 2 ,..., 

% December -> 12)

% monthfork just selects/"spits out" an undelimited argument that 

% comes  behind a delimited argument's delimiter which is formed by 

% a list of all months.

% In any case there will be only one place where the list

% is correct and where the delimiter will match...

% ! is used both for making visibly distinguishing month-phrases 

% from each other more easy and for denoting where the

% remainder which is to be removed by the !!!!-delimited argument

% ends.

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

newcommand*monthtonumber[1]{%

  monthfork

  !#1!February!March!April!May!June!July!August!September!October!November!December!{1}%

  !January!#1!March!April!May!June!July!August!September!October!November!December!{2}%

  !January!February!#1!April!May!June!July!August!September!October!November!December!{3}%

  !January!February!March!#1!May!June!July!August!September!October!November!December!{4}%

  !January!February!March!April!#1!June!July!August!September!October!November!December!{5}%

  !January!February!March!April!May!#1!July!August!September!October!November!December!{6}%

  !January!February!March!April!May!June!#1!August!September!October!November!December!{7}%

  !January!February!March!April!May!June!July!#1!September!October!November!December!{8}%

  !January!February!March!April!May!June!July!August!#1!October!November!December!{9}%

  !January!February!March!April!May!June!July!August!September!#1!November!December!{10}%

  !January!February!March!April!May!June!July!August!September!October!#1!December!{11}%

  !January!February!March!April!May!June!July!August!September!October!November!#1!{12}%

  !!!!%

}%

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

% monthfork grabs the undelimited argument behind that

% list of months that is correct/in correct order due to insertion

% of the name of the month by monthtonumber.

% As monthfork needs to be an argument that processes

% delimited arguments, it needs to be defined in terms of

% def. Nonetheless provide a dummy-definition in terms

% of newcommand before for triggering an error-message

% in case one is about to override a macro that already

% is defined, e.g., by some package.

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

newcommandmonthfork{}%

defmonthfork#1!January!February!March!April!May!June!%

                 July!August!September!October!November!%

                 December!#2#3!!!!{#2}%

%

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

% comparedatetotoday{<month as word><space><day as number>,<space><year as number>}%

% {<tokens in case dates do not differ>}%

% {<tokens in case dates differ>}%

% converts <month as word> to a number and compares that to the value of month,

% compares <day as number> to the value of day,

% compares <year as number> to the value of year

% In case a difference is detected delivers <tokens in case dates differ>

% In case no difference is detected delivers <tokens in case dates do not differ>

% The macro splitdateandcomparecomponents is used for obtaining

% the components of the date.

% As the date is provided in the pattern 

% <month as word><space><day as number>,<space><year as number>

% a space is attached at the end which yields the pattern

% <month as word><space><day as number>,<space><year as number><space>

% and then the components of that pattern are obtained by the macro

% splitdateandcomparecomponents where the three arguments are delimited

% accordingly. Again first a newcommand-dummy-definition for

% triggering error-message in case of overriding an already  existing

% command.

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

newcommandcomparedatetotoday[1]{splitdateandcomparecomponents#1 }%

newcommandsplitdateandcomparecomponents{}%

defsplitdateandcomparecomponents#1 #2, #3 {%

  ifnumthemonth=monthtonumber{#1} %

  expandafter@firstofoneelseexpandafter@secondoftwofi

  {%

    ifnumtheday=#2 %

    expandafter@firstofoneelseexpandafter@secondoftwofi

    {%

      ifnumtheyear=#3 %

      expandafter@firstoftwoelseexpandafter@secondoftwofi

      {@firstoftwo}%

    }%

  }%

  @secondoftwo

}%

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

% comparedatestotoday{%

%    {{<month 1 as word><space><day 1 as number>,<space><year 1 as number>}}%<-date1

%    {{<month 2 as word><space><day 2 as number>,<space><year 2 as number>}}%<-date2

%    ...

%    {{<month k as word><space><day k as number>,<space><year k as number>}}%<-datek

% }%

% {<tokens in case at least one date does not differ from the date formed by

%  year, month and day>}%

% {<tokens in case all dates do differ from the date formed by

%  year, month and day>}%

%

%  comparedatestotoday attaches the token relax to the list of

%  holiday-dates and prepends an argument holding the token 

%  @secondoftwo and calls  comparedatestotodayloop.

%

%  comparedatestotodayloop in a recursive loop compares with all 

%  elements of the list of holiday-dates compares the date-components to

%  month, day, year for finding out if month, day and year 

%  denote one of these holiday-dates.

% 

%  comparedatestotodayloop's recursive loop works as follows:

%

%  comparedatestotodayloop processes two arguments.

%  The first argument denotes the action in case the end of the list is reached.

%  The second argument either is an element of the list of dates or is the

%  attached token relax.

%  Thus for finding out whether the end of the list is reached, one can

%  check whether the second argument equals relax. 

%  If so, just spit out the first argument which denotes the action in

%  case the end of the list is reached.

%  If not so, compare the date held in the second argument to 

%  month, day, year (which are components of today) for finding out 

%  if today is a holiday and therefore the first argument needs to be

%  replaced by @firstoftwo before doing the next iteration by

%  calling comparedatestotodayloop again...

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

newcommandcomparedatestotoday[1]{%

  comparedatestotodayloop{@secondoftwo}#1relax

}%

% comparedatestotodayloop{<token in case end of list is reached>}%

%                         {<either element of list of holiday-dates 

%                           or relax which was attached for marking

%                           the end of the list of holiday-dates>}%

newcommandcomparedatestotodayloop[2]{%

  ifxrelax#2expandafter@firstoftwoelseexpandafter@secondoftwofi

  {#1}{%

    comparedatetotoday{#2}%

                       {comparedatestotodayloop{@firstoftwo}}%

                       {comparedatestotodayloop{#1}}%

  }%

}%

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

% Section: Code for printing lists of dates.

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

% PrintListOfHolidays[<macro for formatting a date>]%

%                     {<separator between dates>}%

%                     {<separator for the last date>}%

%                     {<macro holding the list of dates>}

newcommandexchange[2]{#2#1}

newcommandPrintListOfHolidays[4][RemoveDaysLeadZero]{%

  expandafterexchangeexpandafter{#4}{Holidayloop{#1}{}{}{#2}{#3}}relaxrelax

}%

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

% Holidayloop{<macro for formatting a date>}%

%              {<separator for this date in case it is not the last date of the list>}%

%              {<separator for this date in case it is the last date of the list>}%

%              {<separator between dates>}%

%              {<separator for the last date>}%

%              {<month as word><space><day as number>,>space><year as number>}

% At first glimpse the arguments <separator for this date in case it is not the last date of the list>

% and  <separator between dates> respective

% <separator for this date in case it is the last date of the list> and

% <separator for the last date> seem to be the same. 

% But we must consider the case of the list being empty or holding

% only one element: In these cases we don't want any separator, thus

% we need a possibility to pass empty arguments for the first 

% iteration... 

%

newcommandHolidayloop[7]{%

  ifxrelax#6expandafter@gobbleelseexpandafter@firstofonefi

  {%

    ifxrelax#7expandafter@firstoftwoelseexpandafter@secondoftwofi

    {#3#1{#6}Holidayloop{#1}{#4}{#5}{#4}{#5}{#7}}%<-case: last date of the list

    {#2#1{#6}Holidayloop{#1}{#4}{#5}{#4}{#5}{#7}}%<-case: not the last date of the list

  }%

}%

% macros for formatting the date.

% They all take the date and use "inner" macros that by means of

% delimited arguments split it into components and do the desired

% things to the components.

newcommandRemoveDaysLeadZero[1]{innerRemoveDaysLeadZero#1relax}

newcommandinnerRemoveDaysLeadZero{}%

definnerRemoveDaysLeadZero#1 #2,#3relax{mbox{#1 number#2,#3}}%

%

newcommandRemoveYear[1]{innerRemoveyear#1relax}

newcommandinnerRemoveyear{}%

definnerRemoveyear#1 #2,#3relax{mbox{#1 number#2}}%

%

newcommandAddDayOfWeek[1]{innerAddDayOfweek#1relax}

newcommandinnerAddDayOfweek{}%

definnerAddDayOfweek#1 #2, #3relax{%

   setdatenumber{#3}{monthtonumber{#1}}{#2}%

   mbox{datedayname, #1 #2, #3}%

}%

%

% As we need to compare each today/each combination of

% year, month and day to the list of holidays for

% for finding out whether a today is on a holiday, we can

% maintain a list of such todays that are on holidays.

% Whenever such a today is found, it will added to the macro

% @DaysAffectedByHolidays. That macro in turn is used at the

% end of the document for writing to .aux-file a directive

% for defining a macro DaysAffectedByHolidays that holds the

% list of only those holidays that "collide" with lecture-days.

%

newcommandDaysAffectedByHolidays{}%

newcommand@DaysAffectedByHolidays{}%

AtEndDocument{%

  immediatewrite@auxout{%

    stringgdefstringDaysAffectedByHolidays{@DaysAffectedByHolidays}%

  }%

}%



newififfirst

firsttrue



newcounter{lecture}



newlengthscratchlength



newcommand{nextlec}{%

  iffirst

    firstfalse

  else

    AdvanceDate[7]%

  fi

  % Compare the advanced today to each element of the list of holidays:

  expandaftercomparedatestotoday

  expandafter{Holidaylist}{%

    %

    % Tokens in case the advanced today denotes one of the holidays:

    % 

    %setdatenumber{year}{month}{day}%

    %section*{Holiday: datedayname, today} Holiday.%

    xdef@DaysAffectedByHolidays{@DaysAffectedByHolidays{today}}%

    % calculate another lecture-day...

    nextlec

  }{%

    %

    % Tokens in case the advanced today does not denote one of the holidays:

    % 

   stepcounter{lecture}%

   setdatenumber{year}{month}{day}%

   section*{Lecture~arabic{lecture}: datedayname, today}%

  }%

}%



makeatother



%... Set the first lecture date

ThisYear{2019}

ThisMonth{3}

ThisDay{1}



newcommand*Holidaylist{%

  {March 08, 2019}%

  {March 29, 2019}%

  {April 18, 2019}%

  {May 17, 2019}%

  {June 18,  2019}%

}%



begin{document}



settowidthscratchlength{hbox{textbf{All holidays: }}}

setlengthscratchlength{-scratchlength}

addtolengthscratchlength{textwidth}



% The macros holding the lists of dates of holidays do not

% contain the token relax. Therefore if they are not empty

% as there is at least one holiday, things will end up in

% the else-branch of the if-comparison.

%

ifrelaxHolidaylistrelaxelse

  hbox{%

    hbox{textbf{All holidays: }}%

    hbox toscratchlength{vtop{%

      hsize=scratchlengthnoindent

      PrintListOfHolidays{; }{; }{Holidaylist}.strut%

    }}%

  }%

fi



ifrelaxHolidaylistrelaxelse

  hbox{%

    hbox{textbf{All holidays: }}%

    hbox toscratchlength{vtop{%

      hsize=scratchlengthnoindent

      PrintListOfHolidays[RemoveYear]{, }{ and }{Holidaylist}.strut%

    }}%

  }%

fi



ifrelaxHolidaylistrelaxelse

  hbox{%

    hbox{textbf{All holidays: }}%

    hbox toscratchlength{vtop{%

      hsize=scratchlengthnoindent

      PrintListOfHolidays[AddDayOfWeek]{, }{ and }{Holidaylist}.strut%

    }}%

  }%

fi



% These occur after the 2nd LaTeX-run:



settowidthscratchlength{hbox{textbf{Holidays that affect our lecture-plan: }}}

setlengthscratchlength{-scratchlength}

addtolengthscratchlength{textwidth}



ifrelaxDaysAffectedByHolidaysrelaxelse

  hbox{%

    hbox{textbf{Holidays that affect our lecture-plan: }}%

    hbox toscratchlength{vtop{%

      hsize=scratchlengthnoindent

      PrintListOfHolidays{; }{; }{DaysAffectedByHolidays}.strut%

    }}%

  }%

fi



ifrelaxDaysAffectedByHolidaysrelaxelse

hbox{%

  hbox{textbf{Holidays that affect our lecture-plan: }}%

  hbox toscratchlength{vtop{%

    hsize=scratchlengthnoindent

    PrintListOfHolidays[RemoveYear]{, }{ and }{DaysAffectedByHolidays}.strut%

  }}%

}%

fi



ifrelaxDaysAffectedByHolidaysrelaxelse    

hbox{%

  hbox{textbf{Holidays that affect our lecture-plan: }}%

  hbox toscratchlength{vtop{%

    hsize=scratchlengthnoindent

    PrintListOfHolidays[AddDayOfWeek]{, }{ and }{DaysAffectedByHolidays}.strut%

  }}%

}%

fi



newpage



nextlec

Lecture 01.



nextlec

Lecture 02.



nextlec

Lecture 03.



nextlec

Lecture 04.



nextlec

Lecture 05.



nextlec

Lecture 06.



nextlec

Lecture 07.



nextlec

Lecture 08.



nextlec

Lecture 09.



nextlec

Lecture 10.



end{document}

You can make a list of the holidays and check whether the current date as set by AdvDate appears in the list:

documentclass[twocolumn]{article}

usepackage{advdate}

usepackage{xparse}



ExplSyntaxOn

clist_new:N g_brasil_holiday_clist



NewDocumentCommand{holidays}{m}

 {

  clist_gset:Nn g_brasil_holiday_clist { #1 }

 }

NewDocumentCommand{nextlec}{}

 {

  brasil_check_holiday:

  section*{today}

 }



cs_new_protected:Nn brasil_check_holiday:

 {

  AdvanceDate[7]

  clist_if_in:NxT g_brasil_holiday_clist

   { int_eval:n {day} / int_eval:n {month} }

   { brasil_check_holiday: } % redo the test

 }

cs_generate_variant:Nn clist_if_in:NnT { Nx }

ExplSyntaxOff



holidays{8/3,29/3,18/4,17/5,18/6}



%... Set the first lecture date



ThisYear{2019}

ThisMonth{3}

ThisDay{1}

AdvanceDate[-7]



begin{document}

nextlec

Lecture 01.



nextlec

Lecture 02.



nextlec

Lecture 03.



nextlec

Lecture 04.



nextlec

Lecture 05.



nextlec

Lecture 06.



nextlec

Lecture 07.



nextlec

Lecture 08.



nextlec

Lecture 09.



nextlec

Lecture 10.



nextlec

Lecture 11.



nextlec

Lecture 12.



nextlec

Lecture 13.



nextlec

Lecture 14.



nextlec

Lecture 15.



nextlec

Lecture 16.



nextlec

Lecture 17.



nextlec

Lecture 18.



end{document}

Here I use twocolumn just for reducing the output to a single page.