Add @@ infix operator for LazyList.consLazy

src/FSharpx.Collections.Experimental/AssemblyInfo.fs

@@ -1,6 +1,5 @@
 // Auto-Generated by FAKE; do not edit
 namespace System
-
 open System.Reflection
 open System.Runtime.CompilerServices
 
@@ -15,27 +14,11 @@ open System.Runtime.CompilerServices
 do ()
 
 module internal AssemblyVersionInformation =
-    [<Literal>]
-    let AssemblyTitle = "FSharpx.Collections.Experimental"
-
-    [<Literal>]
-    let AssemblyProduct = "FSharpx.Collections"
-
-    [<Literal>]
-    let AssemblyDescription =
-        "FSharpx.Collections is a collection of datastructures for use with F# and C#."
-
-    [<Literal>]
-    let InternalsVisibleTo = "FSharpx.Collections.Tests"
-
-    [<Literal>]
-    let InternalsVisibleTo_1 = "FSharpx.Collections.Experimental.Tests"
-
-    [<Literal>]
-    let AssemblyVersion = "3.1.0"
-
-    [<Literal>]
-    let AssemblyFileVersion = "3.1.0"
-
-    [<Literal>]
-    let AssemblyConfiguration = "Release"
+    let [<Literal>] AssemblyTitle = "FSharpx.Collections.Experimental"
+    let [<Literal>] AssemblyProduct = "FSharpx.Collections"
+    let [<Literal>] AssemblyDescription = "FSharpx.Collections is a collection of datastructures for use with F# and C#."
+    let [<Literal>] InternalsVisibleTo = "FSharpx.Collections.Tests"
+    let [<Literal>] InternalsVisibleTo_1 = "FSharpx.Collections.Experimental.Tests"
+    let [<Literal>] AssemblyVersion = "3.1.0"
+    let [<Literal>] AssemblyFileVersion = "3.1.0"
+    let [<Literal>] AssemblyConfiguration = "Release"

src/FSharpx.Collections/AssemblyInfo.fs

@@ -1,6 +1,5 @@
 // Auto-Generated by FAKE; do not edit
 namespace System
-
 open System.Reflection
 open System.Runtime.CompilerServices
 
@@ -15,27 +14,11 @@ open System.Runtime.CompilerServices
 do ()
 
 module internal AssemblyVersionInformation =
-    [<Literal>]
-    let AssemblyTitle = "FSharpx.Collections"
-
-    [<Literal>]
-    let AssemblyProduct = "FSharpx.Collections"
-
-    [<Literal>]
-    let AssemblyDescription =
-        "FSharpx.Collections is a collection of datastructures for use with F# and C#."
-
-    [<Literal>]
-    let InternalsVisibleTo = "FSharpx.Collections.Tests"
-
-    [<Literal>]
-    let InternalsVisibleTo_1 = "FSharpx.Collections.Experimental.Tests"
-
-    [<Literal>]
-    let AssemblyVersion = "3.1.0"
-
-    [<Literal>]
-    let AssemblyFileVersion = "3.1.0"
-
-    [<Literal>]
-    let AssemblyConfiguration = "Release"
+    let [<Literal>] AssemblyTitle = "FSharpx.Collections"
+    let [<Literal>] AssemblyProduct = "FSharpx.Collections"
+    let [<Literal>] AssemblyDescription = "FSharpx.Collections is a collection of datastructures for use with F# and C#."
+    let [<Literal>] InternalsVisibleTo = "FSharpx.Collections.Tests"
+    let [<Literal>] InternalsVisibleTo_1 = "FSharpx.Collections.Experimental.Tests"
+    let [<Literal>] AssemblyVersion = "3.1.0"
+    let [<Literal>] AssemblyFileVersion = "3.1.0"
+    let [<Literal>] AssemblyConfiguration = "Release"

src/FSharpx.Collections/FSharpx.Collections.fsproj

@@ -25,6 +25,7 @@
     <Compile Include="Infrastructure.fs" />
     <Compile Include="LazyList.fsi" />
     <Compile Include="LazyList.fs" />
+    <Compile Include="LazyListOperators.fs" />
     <Compile Include="ResizeArray.fsi" />
     <Compile Include="ResizeArray.fs" />
     <Compile Include="Collections.fs" />

src/FSharpx.Collections/LazyListOperators.fs

@@ -0,0 +1,10 @@
+/// Operators for working with LazyList.
+/// This module is opened automatically when FSharpx.Collections is opened.
+[<AutoOpen>]
+module FSharpx.Collections.LazyListOperators
+
+/// O(1). Returns a new LazyList with the given head and a lazy tail.
+/// Infix operator alias for LazyList.consLazy.
+/// Example: <c>let rec ones = 1 @@ lazy ones</c>
+let inline (@@) (head: 'T) (tail: Lazy<LazyList<'T>>) : LazyList<'T> =
+    LazyList.consLazy head tail

tests/FSharpx.Collections.Tests/LazyListTests.fs

@@ -348,6 +348,37 @@ module LazyList =
                   Expect.equal "consLazy infinite" [ 1; 1; 1; 1; 1 ] (LazyList.take 5 ones |> LazyList.toList)
               }
 
+              test "@@ head" {
+                  let tail = lazy (LazyList.ofList [ 2; 3 ])
+                  Expect.equal "@@ head" 1 (LazyList.head(1 @@ tail))
+              }
+
+              test "@@ toList" {
+                  let tail = lazy (LazyList.ofList [ 2; 3 ])
+                  Expect.equal "@@ toList" [ 1; 2; 3 ] (LazyList.toList(1 @@ tail))
+              }
+
+              test "@@ lazy divergence" {
+                  // tail is not evaluated unless the tail is consumed
+                  let mutable tailForced = false
+
+                  let tail =
+                      lazy
+                          (tailForced <- true
+                           LazyList.ofList [ 2; 3 ])
+
+                  let ll = 1 @@ tail
+                  Expect.isFalse "@@ divergence: construction should not force the tail" tailForced
+                  let _ = LazyList.head ll
+                  Expect.isFalse "@@ divergence: head should not force the tail" tailForced
+              }
+
+              test "@@ infinite" {
+                  // build ones = 1 :: 1 :: ... using @@ operator
+                  let rec ones: LazyList<int> = 1 @@ lazy ones
+                  Expect.equal "@@ infinite" [ 1; 1; 1; 1; 1 ] (LazyList.take 5 ones |> LazyList.toList)
+              }
+
               test "takedrop" {
                   Expect.equal "takedrop" [ 4; 5; 6 ]
                   <| LazyList.toList(LazyList.take 3 (LazyList.skip 4 nats))

tests/fable/FSharpx.Collections.Tests/LazyList.test.fs

@@ -19,4 +19,19 @@ let tests =
               let xs = xs |> LazyList.tail |> LazyList.tail
 
               Expect.equal (LazyList.tryHead xs) (Some 3) "should reach third element"
+          }
+
+          test "@@ head" {
+              let tail = lazy (LazyList.ofList [ 2; 3 ])
+              Expect.equal (LazyList.head(1 @@ tail)) 1 "@@ head"
+          }
+
+          test "@@ toList" {
+              let tail = lazy (LazyList.ofList [ 2; 3 ])
+              Expect.equal (LazyList.toList(1 @@ tail)) [ 1; 2; 3 ] "@@ toList"
+          }
+
+          test "@@ infinite" {
+              let rec ones: LazyList<int> = 1 @@ lazy ones
+              Expect.equal (LazyList.take 5 ones |> LazyList.toList) [ 1; 1; 1; 1; 1 ] "@@ infinite"
           } ]