From d1bc42e40d8e9b883b8ee62814f618eb14372494 Mon Sep 17 00:00:00 2001
From: Cyril <sobierajewicz.cyril@gmail.com>
Date: Wed, 23 Dec 2020 22:20:20 +0100
Subject: [PATCH] Add new and run to Record.ST (#71)

* Add Record.ST.new

* Add Record.ST.run

* Copy changes to Foreign.Object.run documentation
---
 src/Record/ST.js   |  8 ++++++++
 src/Record/ST.purs | 11 +++++++++++
 test/Main.purs     |  7 +++----
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/Record/ST.js b/src/Record/ST.js
index 70c20b0..4ea7d15 100644
--- a/src/Record/ST.js
+++ b/src/Record/ST.js
@@ -1,5 +1,13 @@
 "use strict";
 
+exports.run = function (f) {
+  return f();
+};
+
+exports["new"] = function () {
+  return {};
+};
+
 function copyRecord(rec) {
   var copy = {};
   for (var key in rec) {
diff --git a/src/Record/ST.purs b/src/Record/ST.purs
index e68f219..b078723 100644
--- a/src/Record/ST.purs
+++ b/src/Record/ST.purs
@@ -1,5 +1,7 @@
 module Record.ST
   ( STRecord
+  , run
+  , new
   , freeze
   , thaw
   , peek
@@ -21,6 +23,15 @@ foreign import data STRecord :: Region -> Row Type -> Type
 
 type role STRecord nominal representational
 
+-- | Freeze a mutable record, creating an immutable record. Use this function as you would use
+-- | `Control.Monad.ST.run` (from the `purescript-st` package) to freeze a mutable reference.
+-- |
+-- | The rank-2 type prevents the record from escaping the scope of `run`.
+foreign import run :: forall r. (forall h. ST h (STRecord h r)) -> Record r
+
+-- | Create a new, empty mutable record
+foreign import new :: forall h. ST h (STRecord h ())
+
 -- | Freeze a mutable record, creating a copy.
 foreign import freeze :: forall h r. STRecord h r -> ST h (Record r)
 
diff --git a/test/Main.purs b/test/Main.purs
index 606ef76..e98e5e1 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -5,8 +5,7 @@ import Prelude
 import Effect (Effect)
 import Record (delete, equal, get, insert, merge, modify, rename, set)
 import Record.Builder as Builder
-import Control.Monad.ST (run) as ST
-import Record.ST (poke, thaw, freeze, modify) as ST
+import Record.ST (run, poke, thaw, modify) as ST
 import Record.Unsafe (unsafeHas)
 import Test.Assert (assert')
 import Type.Proxy (Proxy(..))
@@ -45,11 +44,11 @@ main = do
       rec <- ST.thaw { x: 41, y: "" }
       ST.poke x 42 rec
       ST.poke y "testing" rec
-      ST.freeze rec
+      pure rec
     stTest2 = ST.run do
       rec <- ST.thaw { x: 41 }
       ST.modify x (_ + 1) rec
-      ST.freeze rec
+      pure rec
 
   assert' "pokeSTRecord" $
     stTest1.x == 42 && stTest1.y == "testing"