From 0217a2129512149f793c809c495ef50597fd2add Mon Sep 17 00:00:00 2001
From: Oskar Gewalli <wallymathieu@users.noreply.github.com>
Date: Fri, 28 May 2021 08:26:42 +0200
Subject: [PATCH] v1 compatibility

---
 src/FSharpPlus/Lens.fs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/FSharpPlus/Lens.fs b/src/FSharpPlus/Lens.fs
index 18d442a9e..c95387cdb 100644
--- a/src/FSharpPlus/Lens.fs
+++ b/src/FSharpPlus/Lens.fs
@@ -52,7 +52,11 @@ module Lens =
     /// <param name="prism">The prism.</param>
     /// <param name="source">The object.</param>
     /// <returns>The value (if any) the prism is targeting.</returns>
+    #if FABLE_COMPILER
     let preview (optic: ('a -> Const<_,'b>) -> _ -> Const<_,'t>) (source: 's) : 'a option = source |> optic (fun x -> Const (First (Some x))) |> Const.run |> First.run
+    #else
+    let preview prism = First.run << Const.run << prism (fun x -> Const (FSharpPlus.Data.First (Some x)))
+    #endif
 
     /// <summary>Build a 'Lens' from a getter and a setter.</summary>
     /// <remarks>The lens should be assigned as an inline function of the free parameter, not a value, otherwise compiler will fail with a type constraint mismatch.</remarks>