Add argument check library

checkarg.lua

@@ -0,0 +1,33 @@
+local function do_check(x, expected_type)
+    if (type(x) ~= expected_type) then
+        error(expected_type .. " expected, got " .. type(x))
+    end
+end
+
+function checknumber(n)
+    do_check(n, "number")
+end
+
+function checkstring(n)
+    do_check(n, "string")
+end
+
+function checknil(n)
+    do_check(n, "nil")
+end
+
+function checkbool(n)
+    do_check(n, "boolean")
+end
+
+function checkuserdata(n)
+    do_check(n, "userdata")
+end
+
+function checkfunc(n)
+    do_check(n, "function")
+end
+
+function checktable(n)
+    do_check(n, "table")
+end