documentation for passing anonymous functions not clear

[sbfnk]

The documentation for passing anonymous functions is not clear. The current documentation for contact_distribution in sim_linelist states that this should be:

any discrete density function that produces non-negative integers

• you wouldn't expect density functions to produce integers - do you mean a random sampler?
• is the function expected to take any arguments, and if yes what should they represent? Do they need to be named?

For infectious_period it only says that it should be

an anonymous function

which is missing the same information - also, does it definitely have to be anonymous? It might help people if these could be pre-defined functions.

It might be good to add an example or two using this approach - when I tried I didn't really know how to do this given the available information. Perhaps copying some of the documentation in epichains would be helpful.