From dc321d25f2780dbe436ccd013dcf986491790950 Mon Sep 17 00:00:00 2001
From: Tyson Williams <tyson.d.w@gmail.com>
Date: Tue, 7 Dec 2021 19:49:01 -0600
Subject: [PATCH] Add some functional programming primitives related to Lazy

---
 src/Hedgehog/GenLazy.fs      | 15 +++++++++++++++
 src/Hedgehog/GenLazyTuple.fs | 10 ++++++++++
 src/Hedgehog/Hedgehog.fsproj |  5 ++++-
 src/Hedgehog/Lazy.fs         | 24 ++++++++++++++++++++++++
 4 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 src/Hedgehog/GenLazy.fs
 create mode 100644 src/Hedgehog/GenLazyTuple.fs
 create mode 100644 src/Hedgehog/Lazy.fs

diff --git a/src/Hedgehog/GenLazy.fs b/src/Hedgehog/GenLazy.fs
new file mode 100644
index 00000000..95120915
--- /dev/null
+++ b/src/Hedgehog/GenLazy.fs
@@ -0,0 +1,15 @@
+// Workaround for a Fable issue: https://github.com/fable-compiler/Fable/issues/2069
+#if FABLE_COMPILER
+module Hedgehog.GenLazy
+#else
+[<RequireQualifiedAccess>]
+module internal Hedgehog.GenLazy
+#endif
+
+let constant a = a |> Lazy.constant |> Gen.constant
+
+let map f = f |> Lazy.map |> Gen.map
+
+let join glgla = glgla |> Gen.bind Lazy.value
+
+let bind f gla = gla |> map f |> join
diff --git a/src/Hedgehog/GenLazyTuple.fs b/src/Hedgehog/GenLazyTuple.fs
new file mode 100644
index 00000000..2cff662c
--- /dev/null
+++ b/src/Hedgehog/GenLazyTuple.fs
@@ -0,0 +1,10 @@
+// Workaround for a Fable issue: https://github.com/fable-compiler/Fable/issues/2069
+#if FABLE_COMPILER
+module Hedgehog.GenLazyTuple
+#else
+[<RequireQualifiedAccess>]
+module internal Hedgehog.GenLazyTuple
+#endif
+
+let mapFst f = f |> Tuple.mapFst |> GenLazy.map
+let mapSnd f = f |> Tuple.mapSnd |> GenLazy.map
diff --git a/src/Hedgehog/Hedgehog.fsproj b/src/Hedgehog/Hedgehog.fsproj
index 202b7160..9f76e133 100644
--- a/src/Hedgehog/Hedgehog.fsproj
+++ b/src/Hedgehog/Hedgehog.fsproj
@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard1.6;netstandard2.0;net45</TargetFrameworks>
@@ -32,6 +32,7 @@ https://github.com/hedgehogqa/fsharp-hedgehog/blob/master/doc/index.md
       <_Parameter1>Hedgehog.Linq.Tests</_Parameter1>
     </AssemblyAttribute>
     <Compile Include="AutoOpen.fs" />
+    <Compile Include="Lazy.fs" />
     <Compile Include="Numeric.fs" />
     <Compile Include="Seed.fs" />
     <Compile Include="Seq.fs" />
@@ -45,6 +46,8 @@ https://github.com/hedgehogqa/fsharp-hedgehog/blob/master/doc/index.md
     <Compile Include="Journal.fs" />
     <Compile Include="Tuple.fs" />
     <Compile Include="GenTuple.fs" />
+    <Compile Include="GenLazy.fs" />
+    <Compile Include="GenLazyTuple.fs" />
     <Compile Include="Outcome.fs" />
     <Compile Include="Report.fs" />
     <Compile Include="PropertyArgs.fs" />
diff --git a/src/Hedgehog/Lazy.fs b/src/Hedgehog/Lazy.fs
new file mode 100644
index 00000000..b72a7eb0
--- /dev/null
+++ b/src/Hedgehog/Lazy.fs
@@ -0,0 +1,24 @@
+// Workaround for a Fable issue: https://github.com/fable-compiler/Fable/issues/2069
+#if FABLE_COMPILER
+module Hedgehog.Lazy
+#else
+[<RequireQualifiedAccess>]
+module internal Hedgehog.Lazy
+#endif
+
+let func (f: unit -> 'a) = Lazy<'a>(valueFactory = fun () -> f ())
+
+let constant (a: 'a) = Lazy<'a>(valueFactory = fun () -> a)
+
+let value (ma: Lazy<'a>) = ma.Value
+
+let map (f: 'a -> 'b) (ma: Lazy<'a>) : Lazy<'b> =
+    (fun () -> ma.Value |> f)
+    |> func
+
+let join (mma: Lazy<Lazy<'a>>) =
+    (fun () -> mma.Value.Value)
+    |> func
+
+let bind (f: 'a -> Lazy<'b>) =
+    f |> map >> join