@@ -34,8 +34,10 @@ local ostime = os.time
 local osdifftime = os.difftime
 local osdate = os.date
 local tonumber = tonumber
+local math = math
 local floor = math.floor
 local log10 = math.log10
+local modf = math.modf
 
 --http://referencesource.microsoft.com/#mscorlib/system/datetime.cs
 local DateTime = {}
@@ -414,7 +416,7 @@ local function parse(s)
             milliseconds = milliseconds / (10 ^ (n - 3))
           else
             local ticks = milliseconds / (10 ^ (n - 7))
-            local _, decimal = math.modf(ticks)
+            local _, decimal = modf(ticks)
             if decimal > 0.5 then
               ticks = ticks + 1
             end
 
@@ -20,6 +20,7 @@ local each = System.each
 
 local io = io
 local open = io.open
+local remove = os.remove
 
 local IOException = System.define("System.IO.IOException", {
   __tostring = System.Exception.ToString,
@@ -94,4 +95,11 @@ function File.Exists(path)
   return file ~= nil
 end
 
+function File.Delete(path)
+  local ok, err = remove(path)
+  if not ok then
+    throw(IOException(err))
+  end
+end
+
 System.define("System.IO.File", File)
@@ -17,9 +17,6 @@ limitations under the License.
 local System = System
 local throw = System.throw
 local Object = System.Object
-local Char = System.Char
-local Int = System.Int
-local Double = System.Double
 local String = System.String
 local Boolean = System.Boolean
 local Delegate = System.Delegate
 
@@ -296,7 +296,7 @@ local function testIO()
   File.WriteAllText(path, s)
   local text = File.ReadAllText(path)
   assert(text == s)
-  os.remove(path)
+  File.Delete(path)
 end
 
 local function testStringBuilder()
@@ -366,9 +366,9 @@ test(testDelegate, "Delegate")
 test(testLinq, "Linq")
 test(testGroupBy, "GroupBy")
 test(testType, "Type")
---test(testNumCast, "NumCast")
---test(testSplit, "testSplit")
---test(testStringBuilder, "StringBuilder")
+test(testNumCast, "NumCast")
+test(testSplit, "testSplit")
+test(testStringBuilder, "StringBuilder")
+test(testIO, "IO")
 --test(testConsole, "Console")
---test(testIO, "IO")
 --test(testAsync, "Async")