* emacs/guix-base.el: Add and use general functions instead of
specialized functions generated by 'guix-define-buffer-type' macro.
(guix-buffer-type, guix-entry-type): New variables.
(guix-set-vars): Add new variables.
(guix-get-show-entries, guix-show-entries, guix-set-buffer)
(guix-history-call, guix-make-history-item)
(guix-get-params-for-receiving, guix-revert-buffer)
(guix-redisplay-buffer): New functions.
(guix-define-buffer-type): Do not generate specialized functions.
* emacs/guix-info.el (guix-package-info-insert-full-names): Use
'guix-get-show-entries'.
(guix-generation-info-insert-number): Likewise.
* emacs/guix-list.el (guix-list-describe): New function.
(guix-list-define-entry-type): Do not generate specialized one.
(guix-generation-list-show-packages): Use 'guix-get-show-entries'.
* emacs/guix.el (guix-show-generations-function): Remove.
(guix-get-show-packages): Use new functions.
(guix-get-show-generations): Likewise.
dfeb023927