On Tue, 18 Dec 2018 06:31:44 -0500
zimoun <zimon.toutoune@gmail.com> wrote:

> What is the convention about license ?
> (license name) or (license license:name)

Just about this point: This is not a "convention", this is part of the
language definition of Guile, the underlying Scheme implementation:

In the module gnu/packes/cran.scm (and many others too) you find:

(define-module (gnu packages cran)
  #:use-module ((guix licenses) #:prefix license:)
  #:use-module (guix packages)
[...]
)

That means: use everything from module "guix licenses" and prefix it
with "license:". So, in the cran module, you must use "license:name" to
use the publicly defined "name" from the "guix licenses" module. 

In other packages that import "guix licenses" without the prefix, you
use "name" directly. See gnu/packages/scsi.scm for an example.

Björn