From f66b87708d10dd22e415e1eaab2feae80a6b0ad7 Mon Sep 17 00:00:00 2001
From: Yura Dupyn <2153100+omedusyo@users.noreply.github.com>
Date: Wed, 18 Feb 2026 01:33:46 +0100
Subject: [PATCH] Update Program.udpate to hot-swap

---
 src/lang/program.ts | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/src/lang/program.ts b/src/lang/program.ts
index 61d9ed0..ed7de18 100644
--- a/src/lang/program.ts
+++ b/src/lang/program.ts
@@ -3,7 +3,7 @@ import { Env, Value } from "./eval/value";
 import { Expr, FunctionName, SignalName, ProductPattern, SignalExpr } from "./expr";
 import { installPrimitives } from "./primitive";
 import { eval_expr } from "./eval/evaluator";
-import { eval_signal_expression, spawnTick, spawnSignal, SignalRuntime, getNode, spawnSource } from "./eval/signalValue"
+import { eval_signal_expression, spawnTick, spawnSignal, SignalRuntime, getNode, spawnSource, hotSwapSignal } from "./eval/signalValue"
 
 export type Timestamp = number;
 
@@ -350,7 +350,7 @@ export namespace Program {
     program.signal_definitions.set(name, { tag: "user", def: newSignal });
     program.signal_definition_order.push(name);
 
-    // TODO: Note that this doesn't actually evaluate the signal and doesn't insert it into signal-runtime.
+    // Note that this doesn't actually evaluate the signal and doesn't insert it into signal-runtime.
     // For that we will use `get_or_create_signal`
 
     return Result.ok(name);
@@ -385,15 +385,9 @@ export namespace Program {
     def.raw_body = raw_body;
     def.lastModifiedAt = Date.now();
 
-    // TODO: When to recompile?
-    // 2. CRITICAL: Invalidate the Runtime Cache
-    // We clear the ID so the next 'read' forces a re-compile.
-    // Note: This does NOT automatically update other signals that 
-    // are currently holding a reference to the *old* signal ID.
-    // That requires a more complex hot-reload strategy, but this 
-    // is the correct first step.
-    def.signalId = undefined;
-    def.is_initializing = false;
+    if (def.signalId !== undefined) {
+      hotSwapSignal(program, def.signalId, body);
+    }
 
     return Result.ok(undefined);
   }