index->string allows printing keystrokes readably

doc/index.md

@@ -99,6 +99,12 @@ To see how commands are implemented, read the code in `command.fnl`.
 There is a simple keymap in `dunlin.fnl`, and you can see the details
 of how keymaps work in `keymap.fnl`
 
+When writing key bindings or printing errors, Dunlin assumes that the
+key producing "Mod 1" (often labelled Alt) is the Meta key, and the
+key producing "Mod 4" (on a PC, typically the key with the Windows logo)
+is the Super key. For me this matches how Emacs does it, but I would
+welcome reports of machines/setups that don't act ths way
+
 
 ## Contributing
 

keymap.fnl

@@ -1,5 +1,6 @@
 (local { : Gdk } (require :lgi))
 (local { : view } (require :fennel))
+(local lume (require :lume))
 
 (local modifier-keyvals
        ;; we need to detect and discard modifier-only key events when
@@ -51,6 +52,25 @@
           (bor m (. Gdk.ModifierType k)))]
     (spec->index {:keyval event.keyval : modmask})))
 
+(fn compact [xs]
+  (icollect [_ v (ipairs xs)] v))
+
+(fn index->string [index]
+  (let [Mod Gdk.ModifierType
+        [keyval modmask] (lume.map (lume.split index ":") tonumber)
+        chars []]
+    (if (> (band modmask Mod.CONTROL_MASK) 0) (table.insert chars "C"))
+    (if (> (band modmask Mod.MOD1_MASK) 0) (table.insert chars "M"))
+    (if (> (band modmask Mod.MOD4_MASK) 0) (table.insert chars "S"))
+    (table.insert chars (Gdk.keyval_name keyval))
+    (table.concat chars  "-")))
+
+(let [v (index->string "103:0")] (assert (= v "g") v))
+(let [v (index->string "65:0")] (assert (= v "A") v))
+(let [v (index->string "120:4")] (assert (= v "C-x") v))
+(let [v (index->string "100:8")] (assert (= v "M-d") v))
+(let [v (index->string "100:12")] (assert (= v "C-M-d") v))
+
 (fn command? [tbl]
   ;; a keymap entry has a string as key, a command
   ;; definition is a numerically-indexed array
@@ -92,7 +112,7 @@
              _
              (do
                (set m keymap)
-               (values nil (.. "No binding for " (view e) " ")))))))
+               (values nil (.. "No binding for " (index->string c) " ")))))))
      }))