Add generic print and println functions to FSharp.Core

.fantomasignore

@@ -75,6 +75,7 @@ src/Compiler/SyntaxTree/LexFilter.fs
 
 src/FSharp.Core/array2.fs
 src/FSharp.Core/array3.fs
+src/FSharp.Core/fslib-extra-pervasives.fs
 src/FSharp.Core/Linq.fs
 src/FSharp.Core/local.fs
 src/FSharp.Core/nativeptr.fs

docs/release-notes/.FSharp.Core/11.0.100.md

@@ -4,3 +4,6 @@
 * Fix `Array.exists2` documentation examples to use equal-length arrays; the previous examples would throw `ArgumentException` at runtime instead of returning the documented `false`/`true` values. ([PR #19672](https://github.com/dotnet/fsharp/pull/19672))
 * Move `Async.StartChild` to the "Starting Async Computations" docs category alongside `Async.StartChildAsTask`. ([Issue #19667](https://github.com/dotnet/fsharp/issues/19667))
 * Add `InlineIfLambda` to `Array.init` ([PR #19869](https://github.com/dotnet/fsharp/pull/19869))
+### Added
+
+* Added generic `print` and `printn` 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))

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

@@ -277,6 +277,23 @@ module ExtraTopLevelOperators =
     let eprintfn format =
         Printf.eprintfn format
 
+    [<CompiledName("PrintValue")>]
+    let inline print (value: 'T) =
+        Console.Out.Write(string value)
+        // Culture-independent types can bypass 'string' and use TextWriter overloads directly.
+        // Numeric types must go through 'string' to ensure InvariantCulture formatting,
+        // since TextWriter.Write(int/float/...) uses the writer's FormatProvider (CurrentCulture).
+        when 'T : string = Console.Out.Write((# "" value : string #))
+        when 'T : char   = Console.Out.Write((# "" value : char #))
+        when 'T : bool   = Console.Out.Write((# "" value : bool #))
+
+    [<CompiledName("PrintValueLine")>]
+    let inline printn (value: 'T) =
+        Console.Out.WriteLine(string value)
+        when 'T : string = Console.Out.WriteLine((# "" value : string #))
+        when 'T : char   = Console.Out.WriteLine((# "" value : char #))
+        when 'T : bool   = Console.Out.WriteLine((# "" value : bool #))
+
     [<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="printn-example">
+    /// <code lang="fsharp">
+    /// printn "Hello, World!"
+    /// // output: Hello, World!
+    /// </code>
+    /// </example>
+    [<CompiledName("PrintValueLine")>]
+    val inline printn: value: 'T -> unit
+
     /// <summary>Print to a string using the given format.</summary>
     ///
     /// <param name="format">The formatter.</param>

tests/FSharp.Compiler.ComponentTests/EmittedIL/PrintFunction.fs

@@ -0,0 +1,98 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace EmittedIL
+
+open Xunit
+open FSharp.Test.Compiler
+
+module PrintFunction =
+
+    [<Fact>]
+    let ``print with int specializes to Int32 ToString with InvariantCulture``() =
+        FSharp """
+module PrintInt
+
+let printInt () = print 42
+         """
+         |> withOptimize
+         |> compile
+         |> shouldSucceed
+         |> verifyIL [
+             """call       class [netstandard]System.IO.TextWriter [netstandard]System.Console::get_Out()"""
+             """call       class [netstandard]System.Globalization.CultureInfo [netstandard]System.Globalization.CultureInfo::get_InvariantCulture()"""
+             """call       instance string [netstandard]System.Int32::ToString(string,"""
+             """callvirt   instance void [netstandard]System.IO.TextWriter::Write(string)"""]
+
+    [<Fact>]
+    let ``printn with int specializes to Int32 ToString with InvariantCulture``() =
+        FSharp """
+module PrintnInt
+
+let printnInt () = printn 42
+         """
+         |> withOptimize
+         |> compile
+         |> shouldSucceed
+         |> verifyIL [
+             """call       class [netstandard]System.IO.TextWriter [netstandard]System.Console::get_Out()"""
+             """call       class [netstandard]System.Globalization.CultureInfo [netstandard]System.Globalization.CultureInfo::get_InvariantCulture()"""
+             """call       instance string [netstandard]System.Int32::ToString(string,"""
+             """callvirt   instance void [netstandard]System.IO.TextWriter::WriteLine(string)"""]
+
+    [<Fact>]
+    let ``print with string calls Write directly``() =
+        FSharp """
+module PrintString
+
+let printStr () = print "hello"
+         """
+         |> withOptimize
+         |> compile
+         |> shouldSucceed
+         |> verifyIL [
+             """call       class [netstandard]System.IO.TextWriter [netstandard]System.Console::get_Out()"""
+             """callvirt   instance void [netstandard]System.IO.TextWriter::Write(string)"""]
+
+    [<Fact>]
+    let ``print with char calls Write char overload``() =
+        FSharp """
+module PrintChar
+
+let printChar () = print 'A'
+         """
+         |> withOptimize
+         |> compile
+         |> shouldSucceed
+         |> verifyIL [
+             """call       class [netstandard]System.IO.TextWriter [netstandard]System.Console::get_Out()"""
+             """callvirt   instance void [netstandard]System.IO.TextWriter::Write(char)"""]
+
+    [<Fact>]
+    let ``print with bool calls Write bool overload``() =
+        FSharp """
+module PrintBool
+
+let printBool () = print true
+         """
+         |> withOptimize
+         |> compile
+         |> shouldSucceed
+         |> verifyIL [
+             """call       class [netstandard]System.IO.TextWriter [netstandard]System.Console::get_Out()"""
+             """callvirt   instance void [netstandard]System.IO.TextWriter::Write(bool)"""]
+
+    [<Fact>]
+    let ``printn with float specializes to Double ToString with InvariantCulture``() =
+        FSharp """
+module PrintnFloat
+
+let printnFloat () = printn 3.14
+         """
+         |> withOptimize
+         |> compile
+         |> shouldSucceed
+         |> verifyIL [
+             """call       class [netstandard]System.IO.TextWriter [netstandard]System.Console::get_Out()"""
+             """call       class [netstandard]System.Globalization.CultureInfo [netstandard]System.Globalization.CultureInfo::get_InvariantCulture()"""
+             """call       instance string [netstandard]System.Double::ToString(string,"""
+             """callvirt   instance void [netstandard]System.IO.TextWriter::WriteLine(string)"""]

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -235,6 +235,7 @@
     <Compile Include="EmittedIL\DebugPointsOnStack\DebugPointsOnStack.fs" />
     <Compile Include="EmittedIL\Enums.fs" />
     <Compile Include="EmittedIL\Literals.fs" />
+    <Compile Include="EmittedIL\PrintFunction.fs" />
     <Compile Include="EmittedIL\NoCompilerInlining.fs" />
     <Compile Include="EmittedIL\RealInternalSignature\ModuleVisibility.fs" />
     <Compile Include="EmittedIL\RealInternalSignature\ModuleInitialization.fs" />

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

@@ -1077,6 +1077,8 @@ 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

@@ -1077,6 +1077,8 @@ 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

@@ -1080,6 +1080,8 @@ 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

@@ -1080,6 +1080,8 @@ 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

@@ -72,6 +72,7 @@
     <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.printn
+
+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 _.``printn writes value followed by newline``() =
+        let result = captureConsoleOut (fun () -> printn "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 _.``printn writes integer with newline``() =
+        let result = captureConsoleOut (fun () -> printn 42)
+        Assert.Equal("42" + Environment.NewLine, result)