How can I cancel Math-mode, which is inside a function, from the outside?

Question

So the problem is simple. A function takes something and puts it inside math-mode ($$). Can I influence that from the outside?

Example:

\documentclass{article}
\def\mathmod#1{$#1$}

\begin{document}
  \mathmod{hello world}
\end{document}

prints this: Is it possible to cancel that mathmode partly from the outside, to make him print something like this: but without moving world out of the function? Maybe there is any command of fixing condition, after which no other command will affect, or something...

Answer 1

Outside \mathmod you use $ to start and end math mode. Inside it, just to the opposite thing: use $ to start and end text mode (take care of the space!).

\documentclass{article}
\def\mathmod#1{$#1$}
\begin{document}
  \mathmod{hello$ world $and$ hello $world\ again}
\end{document}

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PS. You are going to troll most editors with this command ;-) For example, my editor: