1 files changed, 50 insertions, 0 deletions
diff --git a/tex/context/base/mkiv/util-tab.lua b/tex/context/base/mkiv/util-tab.lua
index f395f43de..ed4cef996 100644
--- a/tex/context/base/mkiv/util-tab.lua
+++ b/tex/context/base/mkiv/util-tab.lua
@@ -820,3 +820,53 @@ if setinspector then
     end)
 end
 
+-- ordered hashes (for now here but in the table namespace):
+
+-- local t = table.orderedhash()
+--
+-- t["1"]  = { "a", "b" }
+-- t["2"]  = { }
+-- t["2a"] = { "a", "c", "d" }
+--
+-- for k, v in table.ordered(t) do
+--     ...
+-- end
+
+local mt = {
+    __newindex = function(t,k,v)
+        local n = t.last + 1
+        t.last    = n
+        t.list[n] = k
+        t.hash[k] = v
+    end,
+    __index = function(t,k)
+        return t.hash[k]
+    end,
+    __len = function(t)
+        return t.last
+    end,
+}
+
+function table.orderedhash()
+    return setmetatable({ list = { }, hash = { }, last = 0 }, mt)
+end
+
+function table.ordered(t)
+    local n = t.last
+    if n > 0 then
+        local l = t.list
+        local i = 1
+        local h = t.hash
+        local f = function()
+            if i <= n then
+                local k = i
+                local v = h[l[k]]
+                i = i + 1
+                return k, v
+            end
+        end
+        return f, 1, h[l[1]]
+    else
+        return function() end
+    end
+end