diff --git a/command.fnl b/command.fnl
index 098aacf..f83b459 100644
--- a/command.fnl
+++ b/command.fnl
@@ -5,19 +5,11 @@
 
 (local Buffer (require :buffer))
 
-(fn by-pairs [a]
-  (let [iter (fn [_ a]
-               (match a
-                 [k v & rest] (values rest k v)
-                 _ nil))]
-    (values iter a a)))
-
-(fn define-command [name function ordered-params]
+(fn define-command [name ordered-params function]
   ;; required parameter names and default arguments
-  (let [param-names (icollect [_ name val (by-pairs ordered-params)]
-                      name)
-        params (collect [_ name val (by-pairs ordered-params)]
-                 (values name val))
+  (let [param-names (icollect [_ [name] (pairs ordered-params)] name)
+        params (collect [_ [name completer default] (pairs ordered-params)]
+                 (values name {: completer : default}))
         v {: name
            : function
            : param-names
@@ -26,15 +18,16 @@
 
 (define-command
  "quit-browser"
- #(Gtk.main_quit) [])
+ []
+ #(Gtk.main_quit))
 
 (define-command
  "visit-location"
+ [[:buffer #[$1] (fn [f] f.buffer.name)]
+  [:url  #[$1] #(do "http://www.example.com")]
+  ]
  (fn [{:url url :buffer buffer}]
-   (let [b (Buffer.find buffer)] (: b :visit url)))
- [:buffer (fn [f] f.buffer.name)
-  :url #(do "http://www.example.com")
-  ])
+   (let [b (Buffer.find buffer)] (: b :visit url))))
 
 (fn find-command [name]
   (. commands name))
@@ -102,7 +95,7 @@
      :active s.active
      :error s.error
      :prompt (if s.active (or s.this-param  "Command?" "") "")
-     :default (and param (param self.frame))
+     :default (and param (param.default self.frame))
      }))
 
 (fn update-widget-state [{ : entry : prompt} result]
diff --git a/test/command.fnl b/test/command.fnl
index 888b438..fb1f22b 100644
--- a/test/command.fnl
+++ b/test/command.fnl
@@ -5,12 +5,16 @@
 (var happened false)
 (fn before [] (set happened false))
 
-(Command.define-command "no-args-command" #(set happened true) [])
+(Command.define-command
+ "no-args-command"
+ []
+ #(set happened true))
 
 (Command.define-command
  "multiply"
- (fn [{: a : b }] (set happened (* (tonumber a) (tonumber b))))
- [:a #(do "3") :b #(do "2")])
+ [[:a #[$1] #(do "3")]
+  [:b #[$1] #(do "2")]]
+ (fn [{: a : b }] (set happened (* (tonumber a) (tonumber b)))))
 
 (before)
 (let [commander (Command.commander)