diff --git a/buffer.fnl b/buffer.fnl
index 39a4e6b..36098a3 100644
--- a/buffer.fnl
+++ b/buffer.fnl
@@ -1,4 +1,5 @@
 (local { : Gtk : Gdk : WebKit2 : cairo } (require :lgi))
+(local { : view } (require :fennel))
 
 (fn new-buffer [name]
   (let [props {}
@@ -22,6 +23,7 @@
                                         )))
                                  })]
     {:webview widget
+     :name name
      :visit (fn [self u] (print "visit " u) (widget:load_uri u))
      :properties props}))
 
@@ -32,5 +34,5 @@
             (tset buffers name b)
             b))
    :current (fn [] (let [k (next buffers)] (. buffers k)))
-   :find (fn [self term] (. buffers term))
+   :find (fn [term] (. buffers term))
    })
diff --git a/command.fnl b/command.fnl
index e52feea..010df77 100644
--- a/command.fnl
+++ b/command.fnl
@@ -4,37 +4,90 @@
 (local commands {})
 (local Buffer (require :buffer))
 
-;; when a command is invoked from a binding, the binding may provide
-;; some or all of the parameter values. when there are missing params,
-;; or when invoked from the commander, `invoke` prompts for the
-;; missing params, offering default values which were specified by
-;; define-command
-
 (fn define-command [name function params]
   ;; required parameter names and default arguments
   (let [v {:name name :function function :params params}]
     (tset commands name v)))
 
-(define-command "quit-browser" #(Gtk.main_quit) {})
+(define-command
+ "quit-browser"
+ #(Gtk.main_quit) {})
 
 (define-command
  "visit-location"
  (fn [{:url url :buffer buffer}]
-   (buffer:visit url))
- {:buffer (fn [] (Buffer.current))
+   (let [b (Buffer.find buffer)] (: b :visit url)))
+ {:buffer (fn [] (. (Buffer.current) :name))
   :url #(do "http://www.example.com")
   })
 
-(fn prompt-missing-args [params explicit-args]
-  (collect [k v (pairs params)]
-    (values k (or (. explicit-args k) (v)))))
+(fn find-command [name]
+  (. commands name))
 
-(fn invoke [s args]
-  (match (. commands s)
-    {:function f :params p}
-    (let [prompted-args (prompt-missing-args p args)]
-      (f prompted-args))
-    nil (print "undefined command " s)))
+(local default-state {
+                      :active true
+                      :command nil
+                      :collected-params {}
+                      :this-param nil
+                      })
 
+(var state default-state)
+(fn reset-state []
+  (set state default-state))
 
-{ : invoke }
+(fn next-param [command params]
+  (accumulate [v nil
+               k _ (pairs command.params)
+               &until v]
+    (if (. params k) nil k)))
+
+(fn invoke-command [command params]
+  (command.function params))
+
+(fn next-action [state input-string]
+  (let [state-for-next-param
+        (fn [c params]
+          (match (next-param c params)
+            k1 {
+                :command c
+                :this-param k1
+                :collected-params params
+                :active true
+                }
+        _ (do (invoke-command c params) {:active false})))]
+
+    (match state
+      {:active false} state
+
+      {:command nil}
+      (match (find-command input-string)
+        {: name : params &as c}
+        (state-for-next-param c {})
+
+        nil
+        {
+         :active false
+         :error (.. "can't find command " input-string)
+         })
+
+      {:command c :this-param k :collected-params p}
+      (do
+        (tset p k input-string)
+        (state-for-next-param c p))
+      _
+      (do (print "unexpected state " (view state))
+          state)
+      )))
+
+(fn on-input [str]
+  (let [s (next-action state str)
+        param (if s.active (. (. s.command :params) s.this-param))]
+    (set state s)
+    {
+     :active s.active
+     :error s.error
+     :prompt (or s.this-param  "")
+     :default (and param (param))
+     }))
+
+{ : define-command  : on-input : reset-state }
diff --git a/frame.fnl b/frame.fnl
index c94b0b1..90b6baf 100644
--- a/frame.fnl
+++ b/frame.fnl
@@ -17,9 +17,6 @@
                             :orientation Gtk.Orientation.VERTICAL
                             })
         commander (Gtk.Entry {
-                              :on_activate
-                              (fn [event]
-                                (Command.invoke event.text {}))
                               })
         progress-bar (Gtk.ProgressBar {
                                        :orientation Gtk.Orientation.HORIZONTAL
@@ -30,6 +27,13 @@
                                 :orientation Gtk.Orientation.VERTICAL
                                 })
         ]
+    (tset commander :on_activate
+          (fn [event]
+            (let [result (Command.on-input event.text)]
+              (print "result" (view result))
+              (set commander.placeholder_text (or result.prompt ""))
+              (set commander.text (or result.default "")))))
+
     (doto container
       (: :pack_start commander false false vpad)
       (: :pack_start progress-bar false false vpad)
diff --git a/test/command.fnl b/test/command.fnl
new file mode 100644
index 0000000..7a811e9
--- /dev/null
+++ b/test/command.fnl
@@ -0,0 +1,31 @@
+(local { : view } (require :fennel))
+
+(local Command (require :command))
+
+(var happened false)
+(fn before [] (set happened false) (Command.reset-state))
+
+(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")})
+
+(before)
+(let [(ok err)
+      (match-try (Command.on-input "not-a-command")
+        (where {:error e :active false} (e:match "can't find command")) true
+        (catch
+         x (values nil (view x))))]
+  (assert ok err))
+
+(before)
+(let [(ok err)
+      (match-try (Command.on-input "multiply")
+        {:active true :prompt p1} (Command.on-input "2")
+        {:active true :prompt p2} (Command.on-input "3")
+        (where {:active false} (= happened 6)) true
+        (catch
+         x (values nil (view x))))]
+  (assert ok err))