Fix seq's TryFinally (#544)

Author: gusty

src/FSharpPlus/Control/Monad.fs

@@ -263,8 +263,8 @@ type TryWith =
 type TryFinally =
     inherit Default1
 
-    static member        TryFinally ((computation: unit -> seq<_>        , compensation: unit -> unit), _: Default2, _, _) = seq (try (Seq.toArray (computation ())) finally compensation ())
-    static member        TryFinally ((computation: unit -> NonEmptySeq<_>, compensation: unit -> unit), _: Default2, _, _) = seq (try (Seq.toArray (computation ())) finally compensation ()) |> NonEmptySeq.unsafeOfSeq
+    static member        TryFinally ((computation: unit -> seq<_>        , compensation: unit -> unit), _: Default2, _, _) = seq { try for e in computation () do yield e finally compensation () }
+    static member        TryFinally ((computation: unit -> NonEmptySeq<_>, compensation: unit -> unit), _: Default2, _, _) = seq { try for e in computation () do yield e finally compensation () } |> NonEmptySeq.unsafeOfSeq
 
     [<CompilerMessage(MessageTryFinally, CodeTryFinally, IsError = true)>]
     static member        TryFinally ((_:           unit -> 'R -> _            , _: unit -> unit), _: Default2  , _, _defaults: False) = raise Internals.Errors.exnUnreachable
@@ -305,8 +305,8 @@ type TryFinally with
 type Using =
     inherit Default1
 
-    static member        Using (resource: 'T when 'T :> IDisposable, body: 'T -> seq<'U>        , _: Using) = seq (try Seq.toArray (body resource) finally if not (isNull (box resource)) then resource.Dispose ()) : seq<'U>
-    static member        Using (resource: 'T when 'T :> IDisposable, body: 'T -> NonEmptySeq<'U>, _: Using) = seq (try Seq.toArray (body resource) finally if not (isNull (box resource)) then resource.Dispose ()) |> NonEmptySeq.unsafeOfSeq : NonEmptySeq<'U>
+    static member        Using (resource: 'T when 'T :> IDisposable, body: 'T -> seq<'U>        , _: Using) = seq { try for e in body resource do yield e finally if not (isNull (box resource)) then resource.Dispose () } : seq<'U>
+    static member        Using (resource: 'T when 'T :> IDisposable, body: 'T -> NonEmptySeq<'U>, _: Using) = seq { try for e in body resource do yield e finally if not (isNull (box resource)) then resource.Dispose () } |> NonEmptySeq.unsafeOfSeq : NonEmptySeq<'U>
     static member        Using (resource: 'T when 'T :> IDisposable, body: 'T -> 'R -> 'U , _: Using   ) = (fun s -> try body resource s finally if not (isNull (box resource)) then resource.Dispose ()) : 'R->'U
     static member        Using (resource: 'T when 'T :> IDisposable, body: 'T -> Async<'U>, _: Using   ) = async.Using (resource, body)
     #if !FABLE_COMPILER

tests/FSharpPlus.Tests/ComputationExpressions.fs

@@ -161,6 +161,17 @@ module ComputationExpressions =
 
         // Check the result
         areEquivalent [42] seqValue
+        
+        // Test proper lazyness in for loops
+        let source = seq {
+            yield 1
+            yield 2
+            yield (failwith "error !!!"; 2)
+            yield 3
+        }
+        let x:seq<int> = monad.plus { for x in source do yield x }
+        x.GetEnumerator ()
+        ()
 
     open FsCheck