From 0a8975a2f6c9743c5acf72e0fdcedb669cdad422 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Thu, 21 Dec 2023 10:30:23 +1300
Subject: [PATCH] once asserted ..., once message ..., etc

---
 packages/compiler/src/compiler/codegen.ts | 20 +++++++++++++-------
 packages/compiler/src/compiler/grammar.ts | 10 ++++++++--
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/packages/compiler/src/compiler/codegen.ts b/packages/compiler/src/compiler/codegen.ts
index 202d43f..e4684e8 100644
--- a/packages/compiler/src/compiler/codegen.ts
+++ b/packages/compiler/src/compiler/codegen.ts
@@ -124,6 +124,10 @@ export function expand(tree: Items, ctx: ExpansionContext): Items {
         }
     }
 
+    function facetWrap(t: TemplateFunction, items: Items): Items {
+        return t`__SYNDICATE__.Turn.active.facet(() => {${items}})`;
+    }
+
     function x<T>(p: Pattern<T>, f: (v: T, t: TemplateFunction) => Items) {
         tree = replace(tree, p, (v, start) => f(v, macro.template(fixPos(start))));
     }
@@ -222,8 +226,10 @@ ${joinItems(sa.captureBinders.map(binderTypeGuard(t)), '\n')}
         t`_dataflow(() => {${walk(s.body)}});`);
 
     x(ctx.parser.eventHandlerEndpointStatement, (s, t) => {
+        const wrap = s.once ? (i: Items) => facetWrap(t, i) : (i: Items) => i;
+
         if (s.triggerType === 'dataflow') {
-            return t`__SYNDICATE__.Turn.active._dataflow(() => { if (${walk(s.predicate)}) { ${terminalWrap(t, s.terminal, walk(s.body))} } });`;
+            return wrap(t`__SYNDICATE__.Turn.active._dataflow(() => { if (${walk(s.predicate)}) { ${terminalWrap(t, s.terminal, walk(s.body))} } });`);
         }
 
         if (s.triggerType === 'stop') {
@@ -265,12 +271,14 @@ ${joinItems(sa.captureBinders.map(binderTypeGuard(t)), '\n')}
         })`;
 
         if (s.isDynamic) {
-            return t`__SYNDICATE__.Turn.active.assertDataflow(() => ({
+            return wrap(t`__SYNDICATE__.Turn.active.assertDataflow(() => ({
                 target: currentSyndicateTarget,
                 assertion: ${assertion},
-            }));`;
+            }));`);
         } else {
-            return t`__SYNDICATE__.Turn.active.replace(currentSyndicateTarget, void 0, ${assertion});`;
+            return wrap(
+                t`__SYNDICATE__.Turn.active.replace(currentSyndicateTarget, void 0, ${assertion});`
+            );
         }
     });
 
@@ -286,9 +294,7 @@ ${joinItems(sa.captureBinders.map(binderTypeGuard(t)), '\n')}
 
     xf(ctx.parser.messageSendStatement, (s, t) => t`message(currentSyndicateTarget, ${walk(s.expr)});`);
 
-    xf(ctx.parser.reactStatement, (s, t) => {
-        return t`facet(() => {${s.body}});`;
-    });
+    x(ctx.parser.reactStatement, (s, t) => facetWrap(t, s.body));
 
     x(ctx.parser.stopStatement, (s, t) =>
         t`__SYNDICATE__.Turn.active._stop(__SYNDICATE__.Turn.activeFacet, () => {${walk(s.body)}});`)
diff --git a/packages/compiler/src/compiler/grammar.ts b/packages/compiler/src/compiler/grammar.ts
index 32f2bba..127e8f4 100644
--- a/packages/compiler/src/compiler/grammar.ts
+++ b/packages/compiler/src/compiler/grammar.ts
@@ -52,6 +52,7 @@ export interface StatementTurnAction extends TurnAction {
 
 export interface GenericEventEndpointStatement extends StatementTurnAction {
     terminal: boolean;
+    once: boolean;
     isDynamic: boolean;
 }
 
@@ -278,10 +279,15 @@ export class SyndicateParser {
     readonly eventHandlerEndpointStatement: Pattern<EventHandlerEndpointStatement> =
         this.turnAction(o => {
             o.terminal = false;
+            o.once = false;
             o.isDynamic = true;
             o.body = [];
-            return seq(option(map(atom('stop'), _ => o.terminal = true)),
-                       atom('on'),
+            return seq(alt(seq(option(map(atom('stop'), _ => o.terminal = true)),
+                               atom('on')),
+                           map(atom('once'), _ => {
+                               o.terminal = true;
+                               o.once = true;
+                           })),
                        alt<any>(seq(map(group('(', bind(o as DataflowEndpointStatement, 'predicate',
                                                         this.expr())),
                                         _ => o.triggerType = 'dataflow'),