From 12df5a90efacd898f023718ed53d4df652773bd6 Mon Sep 17 00:00:00 2001
From: kerams <kerams@users.noreply.github.com>
Date: Mon, 29 Dec 2025 10:50:07 +0100
Subject: [PATCH 1/2] Add support for triple quoted ASCII byte string

---
 src/Compiler/lex.fsl                                        | 6 ++++++
 .../Conformance/BasicGrammarElements/BasicConstants.fs      | 6 +++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/Compiler/lex.fsl b/src/Compiler/lex.fsl
index 1f905bc049a..7b8d8735fea 100644
--- a/src/Compiler/lex.fsl
+++ b/src/Compiler/lex.fsl
@@ -1502,6 +1502,12 @@ and tripleQuoteString (sargs: LexerStringArgs) (skip: bool) = parse
       let cont = LexCont.Token(args.ifdefStack, args.stringNest)
       fin.Finish buf kind LexerStringFinisherContext.TripleQuote cont }
 
+ |  '"' '"' '"' 'B'
+    { let (buf, fin, _m, kind, args) = sargs
+      args.interpolationDelimiterLength <- 0
+      let cont = LexCont.Token(args.ifdefStack, args.stringNest)
+      fin.Finish buf { kind with IsByteString = true } LexerStringFinisherContext.TripleQuote cont }
+
  | newline
     { let (buf, _fin, m, kind, args) = sargs
       incrLine lexbuf
diff --git a/tests/fsharp/Compiler/Conformance/BasicGrammarElements/BasicConstants.fs b/tests/fsharp/Compiler/Conformance/BasicGrammarElements/BasicConstants.fs
index 5606ff7bc79..bc9bdc61dad 100644
--- a/tests/fsharp/Compiler/Conformance/BasicGrammarElements/BasicConstants.fs
+++ b/tests/fsharp/Compiler/Conformance/BasicGrammarElements/BasicConstants.fs
@@ -9,8 +9,10 @@ module ``Basic Grammar Element Constants`` =
 
     [<Fact>]
     let ``Basic constants compile `` () =
+        let tripleQuotedByteString = " \"\"\" \" \"\"\"B "
+
         CompilerAssert.Pass 
-            """
+            $"""
 let sbyteConst = 1y
 let int16Const = 1us
 let int32Const = 1ul
@@ -42,6 +44,8 @@ let charConst = '1'
 let stringConst = "1"
     
 let bytestringConst = "1"B
+
+let byteTripleQuotedStringConst = {tripleQuotedByteString}
     
 let bytecharConst = '1'B
     

From b33e00717a6bf92cb8f2684de7b2bd2053b620c4 Mon Sep 17 00:00:00 2001
From: kerams <kerams@users.noreply.github.com>
Date: Mon, 29 Dec 2025 10:59:56 +0100
Subject: [PATCH 2/2] Release notes

---
 docs/release-notes/.FSharp.Compiler.Service/11.0.0.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/release-notes/.FSharp.Compiler.Service/11.0.0.md b/docs/release-notes/.FSharp.Compiler.Service/11.0.0.md
index c8bbf2156ce..5f2d1149fed 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/11.0.0.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/11.0.0.md
@@ -21,6 +21,7 @@
 * Type checker: recover on checking binding parameter constraints ([#19046](https://github.com/dotnet/fsharp/pull/19046))
 * Debugger: provide breakpoint ranges for short lambdas ([#19067](https://github.com/dotnet/fsharp/pull/19067))
 * FSharpDiagnostic: add default severity ([#19152](https://github.com/dotnet/fsharp/pull/19152))
+* Add support for triple quoted ASCII byte string ([#19182](https://github.com/dotnet/fsharp/pull/19182))
 
 ### Changed