Question

I thought that

:folddoc execute v:foldstart."p"

would work, but it only repeatedly returns the first line of just one of the folds.

Thanks.

Answer 1

The first line of a closed fold can be detected using the foldclosed()
function. For a given line number inside of a closed fold, it returns
the number of the line that fold starts on; otherwise, it returns -1.
Obviously, if a line’s number equals to the value of foldclosed()
for that number, then the line is the first one in a fold. In
Vimscript this test can be written as

foldclosed('.') == line('.')

Therefore, to print the first lines of all closed folds, one can use
the following command:

:folddoc if foldclosed('.') == line('.') | # | endif

(Use the :p command instead of the :# one when displaying line
numbers is not necessary.)