Add MergeSources to property CE

CHANGELOG.md

@@ -3,7 +3,7 @@
 - Add `Tree.apply`. Change `Gen.apply` from monadic to applicative. Revert runtime optimization of `Gen.integral`. ([#398][398], [@TysonMN][TysonMN])
 - Change `ListGen.traverse` from monadic to applicative. ([#399][399], [@TysonMN][TysonMN])
 - Fix bug in the `BindReturn` method of the `property` CE where the generated value is not added to the Journal. ([#401][401], [@TysonMN][TysonMN])
-- Add `BindReturn` to the `gen` CE. This essentially changes the last call to `let!` to use `Gen.map` instead of `Gen.bind`. Add `MergeSources` to the `gen` CE.  This change enables the `and!` syntax.
+- Add `BindReturn` to the `gen` CE. This essentially changes the last call to `let!` to use `Gen.map` instead of `Gen.bind`. Add `MergeSources` to the `gen` and `property` CEs.  This change enables the `and!` syntax. ([#400][400], [@TysonMN][TysonMN])
 
 ## Version 0.12.0 (2021-12-12)
 
@@ -194,6 +194,8 @@
 
 [401]:
   https://github.com/hedgehogqa/fsharp-hedgehog/pull/401
+[400]:
+  https://github.com/hedgehogqa/fsharp-hedgehog/pull/400
 [399]:
   https://github.com/hedgehogqa/fsharp-hedgehog/pull/399
 [398]:

src/Hedgehog/Property.fs

@@ -330,6 +330,9 @@ module PropertyBuilder =
             |> Property.ofGen
             |> Property.map f
 
+        member __.MergeSources(ga, gb) =
+            Gen.zip ga gb
+
         member __.ReturnFrom(m : Property<'a>) : Property<'a> =
             m
 

tests/Hedgehog.Tests/PropertyTests.fs

@@ -110,4 +110,25 @@ let propertyTests = testList "Property tests" [
 
         actual =! "false"
 
+    testCase "and! syntax is applicative" <| fun () ->
+        // Based on https://well-typed.com/blog/2019/05/integrated-shrinking/#:~:text=For%20example%2C%20consider%20the%20property%20that
+        let actual =
+            property {
+                let! x = Range.constant 0 1_000_000_000 |> Gen.int32
+                and! y = Range.constant 0 1_000_000_000 |> Gen.int32
+                return x <= y |> Expect.isTrue
+            }
+            |> Property.report
+            |> Report.render
+            |> (fun x -> x.Split ([|Environment.NewLine|], StringSplitOptions.None))
+            |> Array.item 1
+
+        let actual =
+            // normalize printing of a pair between .NET and Fable/JS
+            actual.Replace("(", "")
+                  .Replace(" ", "")
+                  .Replace(")", "")
+
+        actual =! "1,0"
+
 ]