Some initial work.

luprex/main.lua

@@ -0,0 +1,101 @@
+
+inspect = require("inspect")
+
+
+-- If t is a table, return it.  If not, return a blank table.
+function forcetable(t)
+    if type(t) == "table" then
+        return t
+    else
+        return {}
+    end
+end
+
+-- Clear the table out.  Deletes all keys, removes any metatable.
+-- TODO: this doesn't work on tables that have __metatable metamethod.
+function rawclear(t)
+    for k in pairs(t) do
+        rawset(t, k, nil)
+    end
+    setmetatable(t, nil)
+    return t
+end
+
+-- given a class database, removes all the functions that have
+-- been inserted into it, but keeps the class and action tables.
+function reset_class_db(db)
+    for name,maybeclass in pairs(db) do
+        local class = forcetable(maybeclass)
+        local action = forcetable(rawget(class, "action"))
+        rawclear(class)
+        rawclear(action)
+        rawset(db, name, class)
+        class.action = action
+        class.__index = class
+        class.__class = name
+    end
+end
+
+-- Given a class_db, makes an accessor that fetches classes
+-- from that class db.
+function make_class_accessor(db)
+    return function(name)
+        local class = rawget(db, name)
+        if type(class) ~= "table" then
+            class = {}
+            rawset(db, name, class)
+            class.action = {}
+            class.__index = class
+            class.__class = name
+        end
+        return class
+    end
+end
+
+-- given a global_db, makes an accessor that fetches named
+-- tables from that global_db.
+function make_global_accessor(db)
+    return function(name)
+        local global = rawget(db, name)
+        if type(global) ~= "table" then
+            global = {}
+            rawset(db, name, global)
+        end
+        return global
+    end
+end
+
+-- The sandbox list - a list of the builtin functions that gets imported
+-- into world models.  This is a very weak form of sandboxing, a world
+-- model can still easily use functions that are not on this list.  If you
+-- want stronger sandboxing, you need to not link in certain builtins at all.
+--
+-- Omitted from this list: "debug", "dofile", "getfenv", "io", "jit",
+-- "load", "loadfile", "loadstring", "module", "newproxy", "os", "package",
+-- "pcall", "require", "xpcall"
+--
+local sandbox_list = { "assert", "bit", "error", "getmetatable", "inspect",
+    "ipairs", "math", "next", "pairs", "print", "rawequal", "rawget", "rawset",
+    "select", "setmetatable", "tonumber", "tostring", "type", "unpack" }
+
+-- Make a world model.
+--
+function make_world_model()
+    genv = {}
+    genv._G = genv
+    meta = {}
+    meta.class_db = {}
+    meta.global_db = {}
+    meta.source_db = {}
+    meta.tangible_db = {}
+    meta.__newindex = function() error("Global environment is read-only") end
+    -- meta.__metatable = false
+    genv.class = make_class_accessor(meta.class_db)
+    genv.global = make_global_accessor(meta.global_db)
+    for i,name in ipairs(sandbox_list) do
+        genv[name] = _G[name]
+    end
+    setmetatable(genv, meta)
+    return genv
+end
+