From 320cb894f135332fde7e580bc8a83891dfd725b6 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Thu, 30 May 2019 14:06:40 +0100
Subject: [PATCH] Friendlier accessors

---
 implementations/javascript/src/values.js | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/implementations/javascript/src/values.js b/implementations/javascript/src/values.js
index ef4d6d4..ac268f6 100644
--- a/implementations/javascript/src/values.js
+++ b/implementations/javascript/src/values.js
@@ -373,6 +373,15 @@ Record.makeBasicConstructor = function (label, fieldNames) {
   ctor.isClassOf = (v) => ((v instanceof Record) &&
                            is(label, v.label) &&
                            v.fields.size === arity);
+  fieldNames.forEach((name, i) => {
+    ctor['_'+name] = function (r) {
+      if (!ctor.isClassOf(r)) {
+        throw new Error("Record: attempt to retrieve field "+label+"."+name+
+                        " from non-"+label+": "+(r && r.toString()));
+      }
+      return r.get(i);
+    };
+  });
   return ctor;
 };