Hi Ning!
ningyuan...@gmail.com writes:
> Hi all,
>
> I was wondering what is the meaning of symbols prefixed with "#$", for
> example "#$version" in Guix package definitions.
>
> I was trying to write a package definition for a python package whose
> version number was intended to be inferred from git metadata during build
> time via versioneer. However, since Guix does not retain git metadata
> during build, the setup.py statement declaring the version number as to be
> inferred from git metadata had to be changed to refer to a simple version
> number string. I wrote,
>
> #+begin_src
> (arguments
> '(#:phases (modify-phases %standard-phases
> (add-after 'unpack 'amend-version
> (lambda _
> (substitute* "setup.py"
> (("versioneer.get_version\\(\\)")
> (string-append "\"" #$version "\"")))))
> #+end_src
>
> With reference to a patch describing the same issue with a different python
> package with the same inferred git metadata version number issue:
> https://issues.guix.gnu.org/63628#0-lineno26.
>
> However, I get an error I do not understand:
>
> #+begin_src
> starting phase `amend-version'
> error: in phase 'amend-version': uncaught exception:
> unbound-variable #f "Unbound variable: ~S" (ungexp) #f
> #+end_src
>
> I thought I could begin to debug this by understanding what "#$" means in
> "#$version".
The problem in your package definition is that you use an ungexp form outside
of a gexp form. The correct code could be (untested):
(arguments
(list
#:phases
#~(modify-phases %standard-phases
(add-after 'unpack 'amend-version
(lambda _
(substitute* "setup.py"
(("versioneer.get_version\\(\\)")
(string-append "\"" #$version "\"")))))
As already mentioned by Robby #$version is equivalent to (ungexp version) and
similar to quasiquotation in Scheme.
Also: Be sure to import the (guix gexp) module. Otherwise gexp and ungexp might
not be defined.
Best
--
Daniel
