Getting readline to work in scheme-sandbox

[Knute Snortum]

I recently discovered the scheme-sandbox in LilyPond and I want to get
line editing to work.  In scheme-sandbox.ly the comments say:

% One typical thing you might want to put there is
% (use-modules (ice-9 readline))
% (activate-readline)
% in order to activate command line editing for interactive sessions.

I'm assuming that these are commands to type into the sandbox.  But
when I do this I get an error:

guile> (use-modules (ice-9 readline))
ERROR: readline is not provided in this Guile installation
ABORT: (misc-error)

When I search for installed packages at the Linux command line, I see this:

libreadline8/eoan,now 8.0-3 amd64 [installed,automatic]

Any idea why readline is not available?

My system is Ubuntu 19.10, Guile is 2.2 and LilyPond is 2.19.83.

---
Knute Snortum
(via Gmail)