Add braces when dealing with a lazy keyword.

src/Fantomas.Tests/Fantomas.Tests.fsproj

@@ -41,6 +41,7 @@
     <Compile Include="FormatAstTests.fs" />
     <Compile Include="LetBindingTests.fs" />
     <Compile Include="NoTrailingSpacesTests.fs" />
+    <Compile Include="LazyTests.fs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Fantomas\Fantomas.fsproj" />

src/Fantomas.Tests/LazyTests.fs

@@ -0,0 +1,34 @@
+module Fantomas.Tests.LazyTests
+
+open NUnit.Framework
+open FsUnit
+open Fantomas.Tests.TestHelper
+
+[<Test>]
+let ``lazy should wrap with ()``() =
+    formatSourceString false """
+let v = // <- Lazy "1"
+    lazy
+        1 |> string""" config
+    |> prepend newline
+    |> should equal """
+let v = // <- Lazy "1"
+    lazy (1 |> string)
+"""
+
+[<Test>]
+let ``lazy should not wrap with () for multiline``() =
+    formatSourceString false """
+let v = // <- Lazy "1"
+    lazy
+        1
+        |> id
+        |> string""" config
+    |> prepend newline
+    |> should equal """
+let v = // <- Lazy "1"
+    lazy
+        1
+        |> id
+        |> string
+"""

src/Fantomas/CodeFormatter.fsx

@@ -321,11 +321,9 @@ let list1 = ["1"]
 let list2 = ["2"]
 
 """
-let list = 
-    list1 
-    @ list2 
-    @ ["a"; "b"] 
-    @ List.map id ["a"; "b"]
+let v = // <- Lazy "1"
+    lazy
+        1 |> string
 """
 |> formatSrc
 

src/Fantomas/CodePrinter.fs

@@ -473,6 +473,13 @@ and genTuple astContext es =
         ))
 
 and genExpr astContext = function
+    | SingleExpr(Lazy, e) -> 
+        // Always add braces when dealing with lazy
+        let addParens = hasParenthesis e || multiline e
+        str "lazy "
+        +> ifElse addParens id sepOpenT 
+        +> breakNln astContext (multiline e) e
+        +> ifElse addParens id sepCloseT
     | SingleExpr(kind, e) -> str kind +> genExpr astContext e
     | ConstExpr(c) -> genConst c
     | NullExpr -> !- "null"