enharmonics depending on context

[Sandeep Gupta]

Hi list,

Is there a scheme snippet that will reprint a sharp as the enharmonic
flat if it appears after a flat, reprint a flat as the enharmonic
sharp if it appears after a sharp, and leave a note alone if it
appears after a natural?  Better yet would be if it always left fis
and bes alone.

Thanks very much,
Sandeep