detect and discard modifier-only key events

for recognising key sequences, we only want  to look at
events containing non-modifier keystrokes

keymap.fnl

@@ -1,6 +1,24 @@
 (local { : Gdk } (require :lgi))
 (local { : view } (require :fennel))
 
+(local modifier-keyvals
+       {
+        ;; These aren't canonical or official, this is just the
+        ;; result of pressing keys on my keyboard. If Gtk/Gdk/GI
+        ;; implemented KeyEvent.is_modifier we wouldn't have to
+        ;; do this
+        65507 :control_l
+        65505 :shift_l
+        269025067 :fn
+        65515 :windows
+        65513 :alt_l
+        65027 :alt_gr
+        65508 :control_r
+        })
+
+(fn modifier? [keyval]
+  (. modifier-keyvals keyval))
+
 (fn keychord->spec [keychord]
   (let [Mod Gdk.ModifierType
         symbol (keychord:match "(%w+)$")
@@ -44,19 +62,20 @@
     {
      :accept-event
      (fn [_ e]
-       (let [c (event->index e)
-             v (. m c)]
-         (if v
-             (if (designates-command? v)
-                 (do
-                   (set m keymap)
-                   v)
-                 (do
-                   (set m v)
-                   (values nil (.. c " "))))
-             (do
-               (set m keymap)
-               (values nil (.. "No binding for " (view e) " "))))))
+       (when (not (modifier? e.keyval))
+         (let [c (event->index e)
+               v (. m c)]
+           (if v
+               (if (designates-command? v)
+                   (do
+                     (set m keymap)
+                     v)
+                   (do
+                     (set m v)
+                     (values nil (.. c " "))))
+               (do
+                 (set m keymap)
+                 (values nil (.. "No binding for " (view e) " ")))))))
      }))