doc: print available modules

cmd/v/v.v

@@ -92,12 +92,15 @@ fn main_v() {
 			return
 		}
 		'doc' {
+			mut mod := ''
 			if args.len == 1 {
 				println('v doc [module]')
-				exit(1)
+			}
+			else if args.len > 1 {
+				mod = args[1]
 			}
 			table := table.new_table()
-			println(doc.doc(args[1], table, prefs))
+			println(doc.doc(mod, table, prefs))
 			return
 		}
 		else {}

vlib/v/doc/doc.v

@@ -26,9 +26,19 @@ pub fn doc(mod string, table &table.Table, prefs &pref.Preferences) string {
 	vlib_path := os.dir(pref.vexe_path()) + '/vlib'
 	mod_path := mod.replace('.', os.path_separator)
 	path := os.join_path(vlib_path, mod_path)
-	if !os.exists(path) {
+	if mod == '' || !os.exists(path) {
+		if mod != '' {
 			println('module "$mod" not found')
-		println(path)
+		}
+		println('\navailable modules:')
+		mut files := os.ls(vlib_path) or {
+			return ''
+		}
+		files.sort()
+		for file in files {
+			println(file)
+		}
+		// println(path)
 		return ''
 	}
 	// vfiles := os.walk_ext(path, '.v')