Add F# examples for System.String.IsNullOrEmpty (#7750)

Add project+modules for F# String.IsNullOrEmpty snippets

Fix F# snippet link

Author: brenoafb

snippets/fsharp/System/String/IsNullOrEmpty/IsNullOrEmpty.fsproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="inoe.fs" />
+    <Compile Include="NullString1.fs" />
+    <Compile Include="NullString2.fs" />
+    <Compile Include="isnullorempty1.fs" />
+  </ItemGroup>
+
+</Project>

snippets/fsharp/System/String/IsNullOrEmpty/NullString1.fs

@@ -0,0 +1,19 @@
+namespace IsNullOrEmpty
+open System
+
+module NullString1 =
+
+    // <Snippet2>
+    let (s: string) = null
+
+    printfn "The value of the string is '%s'" s
+
+    try
+        printfn "String length is %d" s.Length
+    with
+        | :? NullReferenceException as ex -> printfn "%s" ex.Message
+
+    // The example displays the following output:
+    //     The value of the string is ''
+    //     Object reference not set to an instance of an object.
+    // </Snippet2>

snippets/fsharp/System/String/IsNullOrEmpty/NullString2.fs

@@ -0,0 +1,12 @@
+namespace IsNullOrEmpty
+open System
+
+module NullString2 =
+
+    // <Snippet3>
+    let s = ""
+    printfn "The length of '%s' is %d." s s.Length
+
+    // The example displays the following output:
+    //       The length of '' is 0.
+    // </Snippet3>

snippets/fsharp/System/String/IsNullOrEmpty/inoe.fs

@@ -0,0 +1,24 @@
+namespace IsNullOrEmpty
+open System
+
+module Inoe =
+
+    //<Snippet1>
+    let test (s: string): string =
+        if String.IsNullOrEmpty(s)
+        then "is null or empty"
+        else $"(\"{s}\") is neither null nor empty"
+
+    let s1 = "abcd"
+    let s2 = ""
+    let s3 = null
+
+    printfn "String s1 %s" (test s1)
+    printfn "String s2 %s" (test s2)
+    printfn "String s2 %s" (test s3)
+
+    // The example displays the following output:
+    //       String s1 ("abcd") is neither null nor empty.
+    //       String s2 is null or empty.
+    //       String s3 is null or empty.
+    //</Snippet1>

snippets/fsharp/System/String/IsNullOrEmpty/isnullorempty1.fs

@@ -0,0 +1,19 @@
+namespace IsNullOrEmpty
+open System
+
+module IsNullOrEmpty1 =
+
+    // <Snippet1>
+    let testForNullOrEmpty (s: string): bool =
+        s = null || s = String.Empty
+
+    let s1 = null
+    let s2 = ""
+
+    printfn "%b" (testForNullOrEmpty s1)
+    printfn "%b" (testForNullOrEmpty s2)
+
+    // The example displays the following output:
+    //    true
+    //    true
+    // </Snippet1>

xml/System/String.xml

@@ -8368,6 +8368,7 @@ The <xref:System.Runtime.CompilerServices.CompilationRelaxations.NoStringInterni
  :::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.string.isnullorempty/cpp/isnullorempty1.cpp" id="Snippet1":::
  :::code language="csharp" source="~/snippets/csharp/System/String/IsNullOrEmpty/isnullorempty1.cs" interactive="try-dotnet-method" id="Snippet1":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.string.isnullorempty/vb/isnullorempty1.vb" id="Snippet1":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/String/IsNullOrEmpty/isnullorempty1.fs" interactive="try-dotnet-method" id="Snippet1":::
 
  You can use the <xref:System.String.IsNullOrWhiteSpace%2A> method to test whether a string is `null`, its value is <xref:System.String.Empty?displayProperty=nameWithType>,  or it consists only of white-space characters.
 
@@ -8378,6 +8379,7 @@ A string is `null` if it has not been assigned a value (in C++ and Visual Basic)
 :::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.string.isnullorempty/cpp/NullString1.cpp" id="Snippet2":::
 :::code language="csharp" source="~/snippets/csharp/System/String/IsNullOrEmpty/NullString1.cs" interactive="try-dotnet-method" id="Snippet2":::
 :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.string.isnullorempty/vb/NullString1.vb" id="Snippet2":::
+:::code language="fsharp" source="~/snippets/fsharp/System/String/IsNullOrEmpty/NullString1.fs" interactive="try-dotnet-method" id="Snippet2":::
 
 ## What is an empty string?
 
@@ -8386,13 +8388,15 @@ A string is empty if it  is explicitly assigned an empty string ("") or <xref:Sy
 :::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.string.isnullorempty/cpp/NullString1.cpp" id="Snippet3":::
 :::code language="csharp" source="~/snippets/csharp/System/String/IsNullOrEmpty/NullString1.cs" interactive="try-dotnet-method" id="Snippet3":::
 :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.string.isnullorempty/vb/NullString1.vb" id="Snippet3":::
+:::code language="fsharp" source="~/snippets/fsharp/System/String/IsNullOrEmpty/NullString2.fs" interactive="try-dotnet-method" id="Snippet3":::
 
 ## Examples
  The following example examines three strings and determines whether each string has a value, is an empty string, or is `null`.
 
  :::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR/string.isNullOrEmpty/CPP/inoe.cpp" id="Snippet1":::
  :::code language="csharp" source="~/snippets/csharp/System/String/IsNullOrEmpty/inoe.cs" interactive="try-dotnet-method" id="Snippet1":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR/string.isNullOrEmpty/VB/inoe.vb" id="Snippet1":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/String/IsNullOrEmpty/inoe.fs" interactive="try-dotnet-method" id="Snippet1":::
 
  ]]></format>
         </remarks>
@@ -11383,16 +11387,16 @@ This method searches for all newline sequences within the string and canonicaliz
              occurrences of non-Windows newline sequences will be replaced with the sequence CRLF. When
              running on Unix, all occurrences of non-Unix newline sequences will be replaced with
              a single LF character.
-            
+
              It is not recommended that protocol parsers utilize this API. Protocol specifications often
              mandate specific newline sequences. For example, HTTP/1.1 (RFC 8615) mandates that the request
              line, status line, and headers lines end with CRLF. Since this API operates over a wide range
              of newline sequences, a protocol parser utilizing this API could exhibit behaviors unintended
              by the protocol's authors.
-            
+
              This overload is equivalent to calling <xref:System.String.ReplaceLineEndings(System.String)>, passing
              <xref:System.Environment.NewLine> as the <em>replacementText</em> parameter.
-            
+
              This method is guaranteed O(n) complexity, where <em>n</em> is the length of the input string.
 
           ]]></format>
@@ -11435,17 +11439,17 @@ This method searches for all newline sequences within the string and canonicaliz
 This method searches for all newline sequences within the string and canonicalizes them to the
              newline sequence provided by `replacementText`. If `replacementText`
              is <xref:System.String.Empty>, all newline sequences within the string will be removed.
-            
+
              It is not recommended that protocol parsers utilize this API. Protocol specifications often
              mandate specific newline sequences. For example, HTTP/1.1 (RFC 8615) mandates that the request
              line, status line, and headers lines end with CRLF. Since this API operates over a wide range
              of newline sequences, a protocol parser utilizing this API could exhibit behaviors unintended
              by the protocol's authors.
-            
+
              The list of recognized newline sequences is CR (U+000D), LF (U+000A), CRLF (U+000D U+000A),
              NEL (U+0085), LS (U+2028), FF (U+000C), and PS (U+2029). This list is given by the Unicode
              Standard, Sec. 5.8, Recommendation R4 and Table 5-2.
-            
+
              This method is guaranteed O(n * r) complexity, where <em>n</em> is the length of the input string,
              and where <em>r</em> is the length of `replacementText`.