Regarding the "install-plan", I suggest the following syntax:

(SOURCE TARGET [FILTERS])

In the above, FILTERS are optional.

- When SOURCE matches a file or directory without trailing slash, install it to
  TARGET.
  - If TARGET has a trailing slash, install SOURCE basename beneath TARGET.
  - Otherwise install SOURCE as TARGET.

- When SOURCE is a directory with a trailing slash, or when FILTERS are used,
  the trailing slash of TARGET is implied.
  - Without FILTERS, install the full SOURCE _content_ to TARGET.
    The paths relative to SOURCE are preserved within TARGET.
  - With FILTERS among `#:include`, `#:include-regexp`, `#:exclude`,
    `#:exclude-regexp`:
    - With `#:include`, install only the exact subpaths in the list.
    - With `#:include-regexp`, install subpaths matching the regexps in the list.
    - The `#:exclude*` FILTERS work similarly.  Without `#:include*` flags,
      install every subpath but the files matching the `#:exlude*` filters.
      If both `#:include*` and `#:exclude*` are specified, the exclusion is done
      on the inclusion list.

Examples:

- `("foo/bar" "share/my-app/")`: Install bar to "share/my-app/bar".
- `("foo/bar" "share/my-app/baz")`: Install bar to "share/my-app/baz".
- `("foo/" "share/my-app")`: Install the content of foo inside "share/my-app",
  e.g. install "foo/sub/file" to "share/my-app/sub/file".
- `("foo/" "share/my-app" #:include ("sub/file"))`: Install only "foo/sub/file" to "share/my-app/sub/file".
- `("foo/sub" "share/my-app" #:include ("file"))`: Install "foo/sub/file" to "share/my-app/file".

Maybe instead of having two #:include and #:include-regexp we could have just
one #:include in which the list elements have a "marker" that tells whether they
are regexps or not.

Clojure uses #"..." to mark regexps. Does Guile have something similar?
Any other suggestion?

-- 
Pierre Neidhardt
https://ambrevar.xyz/