From 88bfb1373bbe73859de94c8b3e83a73b84eaf268 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Thu, 25 Feb 2021 11:43:38 +0100
Subject: [PATCH] Tweak matcher

---
 actor.ts | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/actor.ts b/actor.ts
index b8dab66..eadaa9c 100644
--- a/actor.ts
+++ b/actor.ts
@@ -176,7 +176,7 @@ export class Turn {
 //---------------------------------------------------------------------------
 
 export function match(p: Pattern, v: Assertion): Bindings | null {
-    const bindings: Bindings = {};
+    let bindings: Bindings = {};
 
     function walk(p: Pattern, v: Assertion): boolean {
         return fold(p, {
@@ -218,12 +218,20 @@ export function match(p: Pattern, v: Assertion): Bindings | null {
                 if ('type' in t) {
                     switch (t.type) {
                         case 'bind':
-                            bindings[t.name] = v;
-                            return walk(t.pattern, v);
+                            if (walk(t.pattern, v)) {
+                                bindings[t.name] = v;
+                                return true;
+                            }
+                            return false;
                         case 'discard':
                             return true;
-                        case 'not':
-                            return !walk(t.pattern, v);
+                        case 'not': {
+                            const savedBindings = bindings;
+                            bindings = {};
+                            const result = !walk(t.pattern, v)
+                            bindings = savedBindings;
+                            return result;
+                        }
                         case 'and':
                             for (const p of t.patterns) {
                                 if (!walk(p, v)) return false;