Sstrhsrtj

C programmers often use constructs like

#ifdef foo

    printf("foo is defined ");

#endif

#ifndef foo

    printf("foo is not defined ");

#endif

to select certain code-paths during the compilation process, by passing the compiler flag like -Dfoo or just sticking a #define foo 0 somewhere in the code.

Is this possible in LaTeX too? So I am looking for something like

ifdef foo{

   short summary, tldr

 }

ifndef foo{

   long explanation

}

This can be particularly helpful for producing short summary documents from existing TeX files containing long descriptions. I would like to be able to pass
something similar to -Dfoo as a compiler flag, or just define the foo somewhere near the top of the Latex file, just as I would do in the C case.

You can use ifdefined to check whether a macro is defined. To check whether a macro is not defined, reverse the conditional by prefixing unless.

documentclass{article}

%newcommandfoo{}

begin{document}



ifdefinedfoo

   short summary, tldr

fi

unlessifdefinedfoo

   long explanation

fi



end{document}

In ConTeXt MkIV you can achieve this behaviour using Modes.

starttext



startmode[foo]

   short summary, tldr

stopmode

startnotmode[foo]

   long explanation

stopnotmode



stoptext

The great thing about ConTeXt modes is that you can switch them on from the command line of the context program.

$ context --mode=foo test.mkvi