add validate file function.

Create an IO file and test script for file validation in library.

DeathSocket/DeathSocket.fsproj

@@ -7,6 +7,8 @@
   <ItemGroup>
     <Content Include="test-img.jpg" />
     <Compile Include="Domain.fs" />
+    <Compile Include="IO.fs" />
+    <Compile Include="Validation.fs" />
     <Compile Include="GridPainter.fs" />
     <None Include="ScratchPad.fsx" />
   </ItemGroup>

DeathSocket/GridPainter.fs

@@ -2,6 +2,8 @@ namespace DeathSocket
 
     module GridPainter =
 
+        open Validation
+
         let applyGridToImage spec =
-            //validateFilePath 
+            validateFilePath |> ignore
             0

DeathSocket/IO.fs

@@ -0,0 +1,2 @@
+module IO
+

DeathSocket/ScratchPad.fsx

@@ -1,11 +1,13 @@
-#load "GridPainter.fs"
+#load "Validation.fs"
+#load "GridPainter.fs"
 
-open DeathSocket
 open System.Drawing
 open System
 open System.Drawing.Imaging
+open Validation
+open DeathSocket
 
-// Initial Idea ==============================================================
+// INITIAL IDEA ===============================================================
 
 // Change the image or its path to suit your purposes.
 let img = Bitmap.FromFile (__SOURCE_DIRECTORY__ + "/test-img.jpg")
@@ -25,9 +27,18 @@ let horizontalLine =
 let pen = new Pen (Brushes.Red, width = (float32 (10)) )
 graphics.DrawLine (pen, verticalLine.[0], verticalLine.[1])
 graphics.DrawLine (pen, horizontalLine.[0], horizontalLine.[1])
-let desktop = Environment.GetFolderPath (Environment.SpecialFolder.Desktop)
-let savePath = desktop + "/test-grid.png" // Change this to suit you.
-img.Save (savePath)
+let formSavePath =
+    let desktop = Environment.GetFolderPath (Environment.SpecialFolder.Desktop)
+    desktop + "/test-grid.png" // Change this to suit you.
+img.Save (formSavePath)
 img.Dispose
 graphics.Dispose
-pen.Dispose
+pen.Dispose
+
+// DEATH SOCKET TESTING =======================================================
+
+let desktop = Environment.GetFolderPath (Environment.SpecialFolder.Desktop)
+let savePath = desktop + "/test-grid.png" // Change this to suit you.
+
+// Throws an exception if no file is found.
+let validationTest = validateFilePath savePath

DeathSocket/Validation.fs

@@ -0,0 +1,10 @@
+module internal Validation
+
+open System.IO
+
+    let validateFilePath path =
+        match File.Exists path with
+        | true -> ()
+        | false ->
+            invalidArg "File Path" "The image can not be loaded because the file path specified does not exist."
+