From 3f62d68babc4b090127903ef69471f690a720b9b Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Sat, 9 Jan 2021 16:33:56 +0100
Subject: [PATCH] union, intersect, subtract

---
 implementations/javascript/src/flex.ts   | 22 ++++++++++++++++++++--
 implementations/javascript/src/values.ts |  4 ++--
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/implementations/javascript/src/flex.ts b/implementations/javascript/src/flex.ts
index 1d098d5..ed4a7c9 100644
--- a/implementations/javascript/src/flex.ts
+++ b/implementations/javascript/src/flex.ts
@@ -97,7 +97,7 @@ export class FlexMap<K, V> implements Map<K, V> {
         return this.items.values();
     }
 
-    [Symbol.toStringTag] = 'FlexMap';
+    get [Symbol.toStringTag]() { return 'FlexMap'; }
 
     equals(other: any, eqv: Equivalence<V> = (v1, v2) => v1 === v2): boolean {
         if (!('size' in other && 'has' in other && 'get' in other)) return false;
@@ -206,7 +206,7 @@ export class FlexSet<V> implements Set<V> {
         return this.items.values();
     }
 
-    [Symbol.toStringTag] = 'FlexSet';
+    get [Symbol.toStringTag]() { return 'FlexSet'; }
 
     equals(other: any): boolean {
         if (!('size' in other && 'has' in other)) return false;
@@ -220,4 +220,22 @@ export class FlexSet<V> implements Set<V> {
     canonicalValues(): IterableIterator<string> {
         return this.items.keys();
     }
+
+    union(other: Set<V>): FlexSet<V> {
+        const result = new FlexSet(this.canonicalizer, this);
+        for (let k of other) result.add(k);
+        return result;
+    }
+
+    intersect(other: Set<V>): FlexSet<V> {
+        const result = new FlexSet(this.canonicalizer);
+        for (let k of this) if (other.has(k)) result.add(k);
+        return result;
+    }
+
+    subtract(other: Set<V>): FlexSet<V> {
+        const result = new FlexSet(this.canonicalizer);
+        for (let k of this) if (!other.has(k)) result.add(k);
+        return result;
+    }
 }
diff --git a/implementations/javascript/src/values.ts b/implementations/javascript/src/values.ts
index 090d081..70f790d 100644
--- a/implementations/javascript/src/values.ts
+++ b/implementations/javascript/src/values.ts
@@ -598,7 +598,7 @@ export class Dictionary<T> extends FlexMap<Value, T> {
         return this.asPreservesText();
     }
 
-    [Symbol.toStringTag] = 'Dictionary';
+    get [Symbol.toStringTag]() { return 'Dictionary'; }
 
     [PreserveOn](encoder: Encoder) {
         if (encoder.canonical) {
@@ -643,7 +643,7 @@ export class Set extends FlexSet<Value> {
         return new Set(this);
     }
 
-    [Symbol.toStringTag] = 'Set';
+    get [Symbol.toStringTag]() { return 'Set'; }
 
     [PreserveOn](encoder: Encoder) {
         if (encoder.canonical) {