Input command arguments from file

Question

I created some new commands that take arguments. Several of my commands take the same (lengthy) arguments. Because of this I put those arguments in a separate file. But I seem unable to input or import these arguments.

main.tex:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\myfirsttask}{m m m g}{
    #1 #2 #3
    % do stuff
    \IfNoValueF{#4}{%
            #4
            % do stuff
    }
}

\NewDocumentCommand{\mysecondtask}{m m m g}{
    #1 #2 #3
    % do stuff
    \IfNoValueF{#4}{%
            #4
            % do stuff
    }
}

\NewDocumentCommand{\myfirst}{m}{
    \expandafter\myfirsttask\input{#1}
}

\NewDocumentCommand{\mysecond}{m}{
    \expandafter\mysecondtask\input{#1}
}
\ExplSyntaxOff

\begin{document}

    \myfirst{argumentsFile}

    \mysecond{argumentsFile}

\end{document}

argumentsFile.tex:

{first argument}%
{second argument}%
{third argument}%
{optional argument}

At first I did not use \expandafter and got:

Runaway argument?
! Paragraph ended before \myfirsttask  was complete.
<to be read again> 
                   \par

I assumed that \myfirsttask and \mysecondtask dit not have enough arguments as the contents of the argumentsFile were not yet inserted. Therefore I added \expandafter as to insert the argumentsFile before expanding \myfirsttask and \mysecondtask. This however gives me

! LaTeX Error: File `-NoValue-.tex' not found.

Type X to quit or <RETURN> to proceed,
or enter new name. (Default extension: tex)

Enter file name: 
! Emergency stop.
<read *> 

l.34    \myfirst{argumentsFile}

I assume that's because the curly braces in my argumentsFile were removed by the expansion of \input???

Does anyone know how I could correctly import/input command arguments?

Answer 1

\input is not expandable in one step (in LaTeX, the \input primitive is).

You can absorb the contents of the file and then deliver it:

\begin{filecontents*}{\jobname-ArgumentsFile}
{first argument}%
{second argument}%
{third argument}%
{optional argument}
\end{filecontents*}

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\myfirsttask}{m m m g}
  {
    #1~#2~#3
    % do stuff
    \IfNoValueF{#4}{%
            (#4)
            % do stuff
    }
  }

\NewDocumentCommand{\myfirst}{m}
  {
    \tl_set_from_file:Nnn \l_tmpa_tl { } { #1 }
    \exp_last_unbraced:NV \myfirsttask \l_tmpa_tl
  }

\ExplSyntaxOff

\begin{document}

\myfirst{\jobname-ArgumentsFile}

\end{document}