Is it acceptable to put programming code as proof in paper?
From what I can guess about the context, I would avoid putting the code in your paper unless:


the code is really short (say no more than half a column);
the code is interesting in itself;
and you know that your average reader understands the language R.


Otherwise, it would probably better to omit the code altogether and write, in a note, something like:


  To those interested, the authors can provide the R code employed to compute the probability density functions described in this work.