example-rcfile.lua

function Set(t)
   local s = {}
   for _,v in pairs(t) do s[v] = true end
   return s
end

function set_contains(t, e)
   return t[e]
end

-- The set of global shortcuts we don't want to swap cmd/alt.

global_excludes = Set{ "shift-cmd-tab",
		       "cmd-tab" }

-- The set of apps we want to consider swapping keys for, with some
-- notable exclusions. The exclusion means that a "cmd-c" will do the
-- normal OS Terminal behaviour. If you omit items then you would
-- have to use "alt-c" to close a terminal window.

apps = {
   Terminal = { exclude = Set{ "shift-cmd-[",
                               "shift-cmd-]",
                               "cmd-c",
                               "cmd-v",
                               "cmd-1",
                               "cmd-2",
                               "cmd-3",
                               "cmd-t",
                               "cmd-n",
                               "cmd-`",
			 } },
   Eclipse  = { exclude = {} },
   Xcode    = { exclude = {} },
   TextMate = { exclude = Set { "cmd-1",
				"cmd-2",
				"cmd-3",
				"cmd-4",
				"cmd-t" ,
				"cmd-fn-right",
				"cmd-fn-left",
			  } },
   ["NX Player for OS X"] = { exclude = Set{} },
   ["Parallels Desktop"] = {},
}

debug = false

dbgprintf = function(s,...)
   if debug then io.write(s:format(...)) end
end

-- Return true to swap cmd/alt, otherwise false.

-- This function is passed a table comprising the following keys:
--
--   key_str_seq	key sequence (e.g., "shift-cmd-e")
--   alt		true if the alt key was pressed
--   fn                 true if the fn key was pressed
--   control            true if the control key was pressed
--   shift              true if the shift key was pressed
--   cmd                true if the command key was pressed
--   keycode		numeric virtual keycode (e.g., 48)
--   appname            the frontmost application (e.g., Terminal)
--
-- The order of the modifier keys in key_str_eq is always:
--   shift control alt cmd fn, separated by a hyphen ("-").

function swap_keys(t)
   -- for i,v in pairs(t) do print(i,v) end
   -- print(t.appname)
   if set_contains(global_excludes, t.key_str_seq) then
      return false
   end
   if not apps[t.appname] then
      return false
   end
   local excludes = apps[t.appname]["exclude"]
   if (excludes ~= nil and set_contains(excludes, t.key_str_seq)) then
      dbgprintf("-- %s: \"%s\", explicitly ignored\n", t.appname, t.key_str_seq)
      return false
   end
   s, n = t.key_str_seq:gsub("cmd", "alt")
   dbgprintf("++ %s: \"%s\" remapped to \"%s\"\n", t.appname, t.key_str_seq, s)
   return true
end