New approach to backend registers

luametalatex-local.lua

@@ -0,0 +1,53 @@
+-- Implement support for local variables.
+
+local stack = {}
+
+local restore_func = 65536 -- Reserved in firstcode
+lua.get_functions_table()[restore_func] = function()
+  local level = assert(stack[tex.currentgrouplevel], 'Out of sync')
+  stack[tex.currentgrouplevel] = nil
+  for t,entries in next, level do
+    for k,v in next, entries do
+      t[k] = v
+    end
+  end
+end
+local lua_call = token.command_id'lua_call'
+local restore_toks = {token.create'atendofgroup', token.new(restore_func, lua_call)}
+local put_next = token.put_next
+local runtoks = tex.runtoks
+local function put_restore_toks()
+  put_next(restore_toks)
+end
+
+return function(t, k, v, global)
+  local l = tex.currentgrouplevel
+  if global then
+    for i=1,l do
+      local level = stack[i]
+      if level then
+        local saved = level[t]
+        if saved then
+          saved[k] = nil
+        end
+      end
+    end
+  elseif l > 0 then
+    local level = stack[l]
+    if not level then
+      level = {}
+      runtoks(put_restore_toks)
+      stack[l] = level
+    end
+
+    local saved = level[t]
+    if not saved then
+      saved = {}
+      level[t] = saved
+    end
+
+    saved[k] = saved[k] or t[k]
+  end
+
+  t[k] = v
+end