Add generic print and println functions to FSharp.Core

Add inline `print: 'T -> unit` and `println: 'T -> unit` to
ExtraTopLevelOperators. These use the existing `string` function for
conversion (InvariantCulture for IFormattable, .ToString() fallback)
and write to Console.Out.

RFC FS-1125

Author: bbatsov

docs/release-notes/.FSharp.Core/10.0.300.md

@@ -2,6 +2,8 @@
 
 ### Added
 
+* Added generic `print` and `println` functions (`'T -> unit`) to `ExtraTopLevelOperators` for simple value printing to stdout. ([RFC FS-1125](https://github.com/fsharp/fslang-design/blob/main/RFCs/FS-1125-print-printn-functions.md), [PR #19265](https://github.com/dotnet/fsharp/pull/19265))
+
 ### Changed
 
 * Added complexity documentation (Big-O notation) to all 462 functions across Array, List, Seq, Map, and Set collection modules. ([PR #19240](https://github.com/dotnet/fsharp/pull/19240))

src/FSharp.Core/fslib-extra-pervasives.fs

@@ -277,6 +277,14 @@ module ExtraTopLevelOperators =
     let eprintfn format =
         Printf.eprintfn format
 
+    [<CompiledName("PrintValue")>]
+    let inline print (value: 'T) =
+        Console.Out.Write(string value)
+
+    [<CompiledName("PrintValueLine")>]
+    let inline println (value: 'T) =
+        Console.Out.WriteLine(string value)
+
     [<CompiledName("DefaultAsyncBuilder")>]
     let async = AsyncBuilder()
 

src/FSharp.Core/fslib-extra-pervasives.fsi

@@ -56,6 +56,33 @@ module ExtraTopLevelOperators =
     [<CompiledName("PrintFormatLineToError")>]
     val eprintfn: format: Printf.TextWriterFormat<'T> -> 'T
 
+    /// <summary>Converts the value to a string using the <c>string</c> operator and writes it to the standard output.</summary>
+    ///
+    /// <param name="value">The value to print.</param>
+    ///
+    /// <example id="print-example">
+    /// <code lang="fsharp">
+    /// print "Hello, "
+    /// print "World!"
+    /// // output: Hello, World!
+    /// </code>
+    /// </example>
+    [<CompiledName("PrintValue")>]
+    val inline print: value: 'T -> unit
+
+    /// <summary>Converts the value to a string using the <c>string</c> operator and writes it to the standard output, followed by a newline.</summary>
+    ///
+    /// <param name="value">The value to print.</param>
+    ///
+    /// <example id="println-example">
+    /// <code lang="fsharp">
+    /// println "Hello, World!"
+    /// // output: Hello, World!
+    /// </code>
+    /// </example>
+    [<CompiledName("PrintValueLine")>]
+    val inline println: value: 'T -> unit
+
     /// <summary>Print to a string using the given format.</summary>
     ///
     /// <param name="format">The formatter.</param>

tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.debug.bsl

@@ -1073,6 +1073,8 @@ Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToStringThenFail[T,TR
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToString[T](Microsoft.FSharp.Core.PrintfFormat`4[T,Microsoft.FSharp.Core.Unit,System.String,System.String])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToTextWriter[T](System.IO.TextWriter, Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormat[T](Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValue[T](T)
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValueLine[T](T)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceExpression[T](Microsoft.FSharp.Quotations.FSharpExpr`1[T])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceUntypedExpression[T](Microsoft.FSharp.Quotations.FSharpExpr)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T[,] CreateArray2D[a,T](System.Collections.Generic.IEnumerable`1[a])

tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.release.bsl

@@ -1073,6 +1073,8 @@ Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToStringThenFail[T,TR
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToString[T](Microsoft.FSharp.Core.PrintfFormat`4[T,Microsoft.FSharp.Core.Unit,System.String,System.String])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToTextWriter[T](System.IO.TextWriter, Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormat[T](Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValue[T](T)
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValueLine[T](T)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceExpression[T](Microsoft.FSharp.Quotations.FSharpExpr`1[T])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceUntypedExpression[T](Microsoft.FSharp.Quotations.FSharpExpr)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T[,] CreateArray2D[a,T](System.Collections.Generic.IEnumerable`1[a])

tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.debug.bsl

@@ -1076,6 +1076,8 @@ Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToStringThenFail[T,TR
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToString[T](Microsoft.FSharp.Core.PrintfFormat`4[T,Microsoft.FSharp.Core.Unit,System.String,System.String])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToTextWriter[T](System.IO.TextWriter, Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormat[T](Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValue[T](T)
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValueLine[T](T)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceExpression[T](Microsoft.FSharp.Quotations.FSharpExpr`1[T])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceUntypedExpression[T](Microsoft.FSharp.Quotations.FSharpExpr)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T[,] CreateArray2D[a,T](System.Collections.Generic.IEnumerable`1[a])

tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.release.bsl

@@ -1076,6 +1076,8 @@ Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToStringThenFail[T,TR
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToString[T](Microsoft.FSharp.Core.PrintfFormat`4[T,Microsoft.FSharp.Core.Unit,System.String,System.String])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormatToTextWriter[T](System.IO.TextWriter, Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T PrintFormat[T](Microsoft.FSharp.Core.PrintfFormat`4[T,System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit])
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValue[T](T)
+Microsoft.FSharp.Core.ExtraTopLevelOperators: Void PrintValueLine[T](T)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceExpression[T](Microsoft.FSharp.Quotations.FSharpExpr`1[T])
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T SpliceUntypedExpression[T](Microsoft.FSharp.Quotations.FSharpExpr)
 Microsoft.FSharp.Core.ExtraTopLevelOperators: T[,] CreateArray2D[a,T](System.Collections.Generic.IEnumerable`1[a])

tests/FSharp.Core.UnitTests/FSharp.Core.UnitTests.fsproj

@@ -73,6 +73,7 @@
     <None Include="FSharp.Core\Microsoft.FSharp.Core\IntConversionsTestGenerator.fsx" />
     <Compile Include="FSharp.Core\Microsoft.FSharp.Core\OptionModule.fs" />
     <Compile Include="FSharp.Core\Microsoft.FSharp.Core\PrintfTests.fs" />
+    <Compile Include="FSharp.Core\Microsoft.FSharp.Core\PrintTests.fs" />
     <Compile Include="FSharp.Core\Microsoft.FSharp.Core\ResultTests.fs" />
     <Compile Include="FSharp.Core\Microsoft.FSharp.Core\ExtraTopLevelOperatorsTests.fs" />
     <Compile Include="FSharp.Core\Microsoft.FSharp.Control\EventTypes.fs" />

tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Core/PrintTests.fs

@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+// Various tests for:
+// Microsoft.FSharp.Core.ExtraTopLevelOperators.print
+// Microsoft.FSharp.Core.ExtraTopLevelOperators.println
+
+namespace FSharp.Core.UnitTests
+
+open System
+open System.IO
+open Xunit
+
+[<Collection(nameof FSharp.Test.NotThreadSafeResourceCollection)>]
+type PrintTests() =
+
+    let captureConsoleOut (f: unit -> unit) =
+        let oldOut = Console.Out
+        use sw = new StringWriter()
+        Console.SetOut(sw)
+        try
+            f ()
+            sw.ToString()
+        finally
+            Console.SetOut(oldOut)
+
+    [<Fact>]
+    member _.``print writes string value``() =
+        let result = captureConsoleOut (fun () -> print "hello")
+        Assert.Equal("hello", result)
+
+    [<Fact>]
+    member _.``print writes integer value``() =
+        let result = captureConsoleOut (fun () -> print 42)
+        Assert.Equal("42", result)
+
+    [<Fact>]
+    member _.``print writes float with InvariantCulture``() =
+        let result = captureConsoleOut (fun () -> print 3.14)
+        Assert.Equal("3.14", result)
+
+    [<Fact>]
+    member _.``print writes bool value``() =
+        let result = captureConsoleOut (fun () -> print true)
+        Assert.Equal("True", result)
+
+    [<Fact>]
+    member _.``print writes Some value``() =
+        let result = captureConsoleOut (fun () -> print (Some 42))
+        Assert.Equal("Some(42)", result)
+
+    [<Fact>]
+    member _.``print writes None value``() =
+        let result = captureConsoleOut (fun () -> print None)
+        Assert.Equal("", result)
+
+    [<Fact>]
+    member _.``print writes list value``() =
+        let result = captureConsoleOut (fun () -> print [1; 2; 3])
+        Assert.Equal("[1; 2; 3]", result)
+
+    [<Fact>]
+    member _.``println writes value followed by newline``() =
+        let result = captureConsoleOut (fun () -> println "hello")
+        Assert.Equal("hello" + Environment.NewLine, result)
+
+    [<Fact>]
+    member _.``multiple prints concatenate``() =
+        let result = captureConsoleOut (fun () ->
+            print "Hello, "
+            print "World!")
+        Assert.Equal("Hello, World!", result)
+
+    [<Fact>]
+    member _.``println writes integer with newline``() =
+        let result = captureConsoleOut (fun () -> println 42)
+        Assert.Equal("42" + Environment.NewLine, result)