From e31ff8b8d0a165b3f403a1269455fa38220821e6 Mon Sep 17 00:00:00 2001
From: Ludovic Courtès <ludo@gnu.org>
Date: Fri, 10 May 2013 12:33:18 +0200
Subject: ui: Implement `guix --help'.

* guix/ui.scm (command-files, commands, show-guix-help): New procedures.
  (guix-main): Invoke `show-guix-help' when passed `--help'.
---
 guix/ui.scm | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/guix/ui.scm b/guix/ui.scm
index 1435575cdd..c26ea06cb4 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -30,6 +30,7 @@ (define-module (guix ui)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-37)
+  #:autoload   (ice-9 ftw)  (scandir)
   #:use-module (ice-9 match)
   #:use-module (ice-9 format)
   #:export (_
@@ -385,10 +386,36 @@ (define (args-fold* options unrecognized-option-proc operand-proc . seeds)
              (apply format #f msg args)))))
 
 (define (show-guix-usage)
-  ;; TODO: Dynamically generate a summary of available commands.
   (format (current-error-port)
           (_ "Usage: guix COMMAND ARGS...~%")))
 
+(define (command-files)
+  "Return the list of source files that define Guix sub-commands."
+  (define directory
+    (and=> (search-path %load-path "guix.scm")
+           (compose (cut string-append <> "/guix/scripts")
+                    dirname)))
+
+  (if directory
+      (scandir directory (cut string-suffix? ".scm" <>))
+      '()))
+
+(define (commands)
+  "Return the list of Guix command names."
+  (map (compose (cut string-drop-right <> 4)
+                basename)
+       (command-files)))
+
+(define (show-guix-help)
+  (format #t (_ "Usage: guix COMMAND ARGS...
+Run COMMAND with ARGS.\n"))
+  (newline)
+  (format #t (_ "COMMAND must be one of the sub-commands listed below:\n"))
+  (newline)
+  ;; TODO: Display a synopsis of each command.
+  (format #t "~{   ~a~%~}" (commands))
+  (show-bug-report-information))
+
 (define program-name
   ;; Name of the command-line program currently executing, or #f.
   (make-parameter #f))
@@ -417,7 +444,7 @@ (define (guix-main arg0 . args)
     (define (option? str) (string-prefix? "-" str))
     (match args
       (() (show-guix-usage) (exit 1))
-      (("--help") (show-guix-usage))
+      (("--help") (show-guix-help))
       (("--version") (show-version-and-exit "guix"))
       (((? option?) args ...) (show-guix-usage) (exit 1))
       ((command args ...)
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