Brendan Tildesley <brendan.tildesley@openmailbox.org> writes:

> From 9202987ba9aed6e7c503aca877110e0e27e3dbc0 Mon Sep 17 00:00:00 2001
> From: Brendan Tildesley <brendan.tildesley@openmailbox.org>
> Date: Sat, 13 May 2017 23:24:06 +1000
> Subject: [PATCH 05/12] gnu: calibre: Unbundle python2-markdown
>
> * gnu/packages/ebook.scm (calibre):
> [snippet]: Replace python references to bundled markdown with packaged. Remove
> markdown from source.
> [inputs]: Add python2-markdown as a dependency.

Nice!

> @@ -78,8 +78,11 @@
>          (modules '((guix build utils)))
>          (snippet
>            '(begin
> +            (delete-file-recursively "src/calibre/ebooks/markdown")
>              (delete-file-recursively "src/unrar")
> -            (delete-file "src/odf/thumbnail.py")))
> +            (delete-file "src/odf/thumbnail.py")
> +            (substitute* (find-files "." "\\.py")
> +              (("calibre\\.ebooks\\.markdown") "markdown"))))

Can you add a #t after this substitution, since its return value is
unspecified?