it's not useful. nix-instantiate will always point to the wrong location
because "at the toplevel" is not a position we can point to. all nesting
conversions will point to strange places: the *original* definition of a
lambda value (or partial applications thereof), or nowhere at all (since
only lambda values can have their positions determined in the formatter)
Change-Id: I56bd9e1cf3cae11b4198f148a141ca758e4fe8ac
eldritch horrors
bdebc3797b