Implement Array.head

commit 5898cc7e82befdbf9b7457f41e898c3b1b916a57
Merge: 173d8336 fec1862
Author: latkin <latkin@microsoft.com>
Date:   Sun Oct 12 10:15:38 2014 -0700

    Merge branch 'hd' of https://git01.codeplex.com/forks/forki/fsharp into PR

    Conflicts:
    	src/fsharp/FSharp.Core.Unittests/SurfaceArea.4.0.fs
    	src/fsharp/FSharp.Core.Unittests/SurfaceArea.Portable.fs

commit fec186272559585de8e47fe070189751906f8553
Author: Steffen Forkmann <steffen.forkmann@msu-solutions.de>
Date:   Wed Jul 2 18:29:27 2014 +0200

    Adding surface areay for Array.head

commit 334166c0ada7d5457f3c77756d192167b5ebf9f1
Author: Steffen Forkmann <steffen.forkmann@msu-solutions.de>
Date:   Wed Jul 2 18:25:36 2014 +0200

    Improve docs for Array.head

commit 9dd524476c8afe127d64d2d2d87ae81cae736737
Author: Steffen Forkmann <steffen.forkmann@msu-solutions.de>
Date:   Wed Jul 2 18:24:40 2014 +0200

    Fixing error message for Array.head

commit b4cf72e2b22b574c28fb7daaf85887546dd06b17
Author: Steffen Forkmann <steffen.forkmann@msu-solutions.de>
Date:   Mon Jun 30 15:56:22 2014 +0200

    implementing "head" for array

src/fsharp/FSharp.Core.Unittests/FSharp.Core/Microsoft.FSharp.Collections/ArrayModule.fs

@@ -962,6 +962,20 @@ type ArrayModule() =
         
         ()
 
+    [<Test>]
+    member this.Hd() =
+        // integer array
+        let resultInt = Array.head [|2..2..20|]
+        Assert.AreEqual(2, resultInt)
+        
+        // string array
+        let resultStr = Array.head [|"a";"b";"c";"d"|] 
+        Assert.AreEqual("a", resultStr)
+            
+        CheckThrowsArgumentException(fun () -> Array.head [||] |> ignore)        
+        CheckThrowsArgumentNullException(fun () -> Array.head null |> ignore)
+        ()    
+
     [<Test>]
     member this.Init() = 
         this.InitTester Array.init Array.init

src/fsharp/FSharp.Core.Unittests/SurfaceArea.4.0.fs

@@ -124,6 +124,7 @@ Microsoft.FSharp.Collections.ArrayModule: T Average[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T ExactlyOne[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T Find[T](Microsoft.FSharp.Core.FSharpFunc`2[T,System.Boolean], T[])
 Microsoft.FSharp.Collections.ArrayModule: T Get[T](T[], Int32)
+Microsoft.FSharp.Collections.ArrayModule: T Head[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T Last[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T MaxBy[T,TResult](Microsoft.FSharp.Core.FSharpFunc`2[T,TResult], T[])
 Microsoft.FSharp.Collections.ArrayModule: T Max[T](T[])

src/fsharp/FSharp.Core.Unittests/SurfaceArea.Portable.fs

@@ -118,6 +118,7 @@ Microsoft.FSharp.Collections.ArrayModule: T Average[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T ExactlyOne[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T Find[T](Microsoft.FSharp.Core.FSharpFunc`2[T,System.Boolean], T[])
 Microsoft.FSharp.Collections.ArrayModule: T Get[T](T[], Int32)
+Microsoft.FSharp.Collections.ArrayModule: T Head[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T Last[T](T[])
 Microsoft.FSharp.Collections.ArrayModule: T MaxBy[T,TResult](Microsoft.FSharp.Core.FSharpFunc`2[T,TResult], T[])
 Microsoft.FSharp.Collections.ArrayModule: T Max[T](T[])

src/fsharp/FSharp.Core/array.fs

@@ -177,7 +177,12 @@ namespace Microsoft.FSharp.Collections
             let res : 'T[] = Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked (n1 + n2)
             Array.Copy(array1, 0, res, 0, n1)
             Array.Copy(array2, 0, res, n1, n2)
-            res            
+            res   
+                     
+        [<CompiledName("Head")>]
+        let head (array : 'T[]) =
+            checkNonNull "array" array
+            if array.Length = 0 then invalidArg "array" InputArrayEmptyString else array.[0]
 
         [<CompiledName("Copy")>]
         let copy (array: 'T[]) =

src/fsharp/FSharp.Core/array.fsi

@@ -322,6 +322,17 @@ namespace Microsoft.FSharp.Collections
         [<CompiledName("Get")>]
         val get: array:'T[] -> index:int -> 'T
 
+        /// <summary>Returns the first element of the array.</summary>
+        ///
+        /// <param name="array">The input array.</param>
+        ///
+        /// <returns>The first element of the array.</returns>
+        ///
+        /// <exception cref="System.ArgumentNullException">Thrown when the input array is null.</exception>
+        /// <exception cref="System.ArgumentException">Thrown when the input array is empty.</exception>
+        [<CompiledName("Head")>]
+        val head: array:'T[] -> 'T
+
         /// <summary>Creates an array given the dimension and a generator function to compute the elements.</summary>
         /// <param name="count">The number of elements to initialize.</param>
         /// <param name="initializer">The function to generate the initial values for each index.</param>