even better sandbox

static/js/components/literate-programming.js

@@ -200,12 +200,25 @@ class OutputMode {
     clearResults() {
         this.frame.replaceChildren();
     }
+
+    static messageOutputArrayToString(output) {
+        return output
+            .map(x => {
+                if (typeof x === "object") return JSON.stringify(x);
+                else return x + "";
+            })
+            .join(" ");
+    }
 }
 
 class GraphicsMode {
     constructor(frame) {
         this.frame = frame;
 
+        this.error = document.createElement("pre");
+        this.error.classList.add("error");
+        this.frame.appendChild(this.error);
+
         this.iframe = document.createElement("iframe");
         this.iframe.classList.add("hidden");
         this.iframe.src = import.meta.resolve("../../html/sandbox.html");
@@ -213,15 +226,20 @@ class GraphicsMode {
 
         this.iframe.contentWindow.addEventListener("message", event => {
             let message = event.data;
-            if (message.kind == "resize") {
+            if (message.kind == "ready") {
+                this.evaluate();
+            }
+            else if (message.kind == "resize") {
                 this.resize(message);
+            } else if (message.kind == "output" && message.output.kind == "error") {
+                this.error.textContent = OutputMode.messageOutputArrayToString(message.output.message);
+                this.iframe.classList.add("hidden");
+            } else if (message.kind == "evalComplete") {
+                this.error.textContent = "";
             }
         });
 
-        this.iframe.contentWindow.addEventListener("DOMContentLoaded", () => this.evaluate());
         this.frame.program.onChanged.push(_ => this.evaluate());
-
-        this.evaluate();
     }
 
     evaluate() {

static/js/components/literate-programming/eval.js

@@ -18,7 +18,22 @@ async function withTemporaryGlobalScope(callback) {
     }
 }
 
-export async function evaluate(commands) {
+let evaluationComplete = null;
+
+export async function evaluate(commands, { start, success, error }) {
+    if (evaluationComplete != null) {
+        await evaluationComplete;
+    }
+
+    if (start != null) {
+        start();
+    }
+
+    let signalEvaluationComplete;
+    evaluationComplete = new Promise((resolve, _reject) => {
+        signalEvaluationComplete = resolve;
+    })
+
     outputIndex = 0;
     try {
         await withTemporaryGlobalScope(async scope => {
@@ -34,15 +49,25 @@ export async function evaluate(commands) {
                 }
             }
         });
-    } catch (error) {
+        if (success != null) {
+            success();
+        }
+        postMessage({
+            kind: "evalComplete",
+        });
+    } catch (err) {
         postMessage({
             kind: "output",
             output: {
                 kind: "error",
-                message: [error.toString()],
+                message: [err.toString()],
             },
             outputIndex,
         });
+        if (error != null) {
+            error();
+        }
     }
+    signalEvaluationComplete();
 }
 

static/js/components/literate-programming/worker.js

@@ -18,6 +18,6 @@ globalThis.console = {
 addEventListener("message", async event => {
     let message = event.data;
     if (message.action == "eval") {
-        evaluate(message.input);
+        evaluate(message.input, {});
     }
 });