--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mcbot/cmds/calc.lua	Sun Apr 11 18:13:18 2010 +0200
@@ -0,0 +1,49 @@
+
+local function sbox (untrusted_code)
+    -- make environment
+    local env = {}
+
+    -- run code under environment
+    local untrusted_function, message = loadstring(untrusted_code)
+    if not untrusted_function then return nil, message end
+    setfenv(untrusted_function, env)
+    local success, result = pcall(untrusted_function)
+    if success then
+        return result
+    else
+        return nil, result
+    end
+end
+
+-- ---- ----
+
+local function dc (args)
+    if not args then return nil, "Give me an expression" end
+    -- Downloaded from http://www.math.bas.bg/bantchev/place/rpn/rpn.lua.html
+    tb = {}  z = 0
+    for tk in string.gmatch(args,'%S+') do
+      if string.find(tk,'^[-+*/]$')  then
+        if 2>#tb then z = nil break end
+        y,x = table.remove(tb),table.remove(tb)
+        loadstring('z=x'..tk..'y')()
+      else
+        z = tonumber(tk)  if z==nil then break end
+      end
+      table.insert(tb,z)
+    end
+    n = #tb
+    if n==1 and z then return z
+    elseif n>1 or z==nil then return nil, "dc: Error!" end
+end
+
+local function calc (args)
+    if not args then return nil, "Give me an expression" end
+    local f, msg = sbox("return "..args)
+    if not f then
+        return nil, "calc: Cannot evaluate expression"
+    end
+    return tostring(f)
+end
+
+mcbot_register_command("dc", dc)
+mcbot_register_command("calc", calc)