emacs: Add code to run guix command in REPL.

* emacs/guix-base.el (guix-run-command-in-repl, guix-command-output,
  guix-help-string): New functions.
* emacs/guix-main.scm (guix-command, guix-command-output, help-string):
  New procedures.

emacs/guix-base.el

@@ -1084,6 +1084,27 @@ FILE.  With a prefix argument, also prompt for PROFILE."
       (concat "--manifest=" file))
      operation-buffer)))
 
+
+;;; Executing guix commands
+
+(defun guix-run-command-in-repl (args)
+  "Execute 'guix ARGS ...' command in Guix REPL."
+  (guix-eval-in-repl
+   (apply #'guix-make-guile-expression
+          'guix-command args)))
+
+(defun guix-command-output (args)
+  "Return string with 'guix ARGS ...' output."
+  (guix-eval-read
+   (apply #'guix-make-guile-expression
+          'guix-command-output args)))
+
+(defun guix-help-string (&optional commands)
+  "Return string with 'guix COMMANDS ... --help' output."
+  (guix-eval-read
+   (apply #'guix-make-guile-expression
+          'help-string commands)))
+
 
 ;;; Pull
 

emacs/guix-main.scm

@@ -930,6 +930,24 @@ GENERATIONS is a list of generation numbers."
         (format #t "The source store path: ~a~%"
                 (package-source-derivation->store-path derivation))))))
 
+
+;;; Executing guix commands
+
+(define (guix-command . args)
+  "Run 'guix ARGS ...' command."
+  (catch 'quit
+    (lambda () (apply run-guix args))
+    (const #t)))
+
+(define (guix-command-output . args)
+  "Return string with 'guix ARGS ...' output."
+  (with-output-to-string
+    (lambda () (apply guix-command args))))
+
+(define (help-string . commands)
+  "Return string with 'guix COMMANDS ... --help' output."
+  (apply guix-command-output `(,@commands "--help")))
+
 
 ;;; Lists of packages, lint checkers, etc.