For example, make the output from preprocess be made available to later functions as preprocess$ elements. For example, outputting NULL would yield preprocess to be NULL.
I suppose I want preprocess to always be the same thing, namely a list. So perhaps if they output a character vector, or a single object (like NULL), then that is just put into a list.
preprocess
be made available to later functions aspreprocess$
elements. For example, outputtingNULL
would yieldpreprocess
to be NULL.