Deeper questions of partiality aside, if a function can throw exceptions, the documentation should spell this out *explicitly*, ideally also specifying what the type of the exception may be. To me, this is a *minimum* standard to expect from documentation in any language with exceptions.
Whenever I write a function that might error out in my work code, I always write a separate paragraph explaining this. Usually it reads something like "Raises an error if these conditions aren't met" for whatever preconditions the function has. I don't know if this documentation requirement is in our style guide, but if it isn't I should put it in :).
This is definitely something we should have in the documentation for base. I would document head something like this:
> Return the first element of the given list.
> Raises an 'ErrorCall' exception if the list is empty.
I could see a case for putting less emphasis on the fact that it's a specific exception—exceptions in pure functions are a bit weird—but the basic structure would still be the same: a distinct part of the documentation calling out the error condition explicitly.