Support key for echo

runtime/index.js

@@ -2,7 +2,7 @@ import {transpileJavaScript} from "@observablehq/notebook-kit";
 import {Runtime} from "@observablehq/runtime";
 import inspector from "object-inspect";
 import {parse} from "acorn";
-import {group} from "d3-array";
+import {group, groups} from "d3-array";
 import {dispatch as d3Dispatch} from "d3-dispatch";
 import * as stdlib from "./stdlib.js";
 import {OUTPUT_MARK} from "./constant.js";
@@ -46,12 +46,16 @@ function inspect(value, {limit = 200, quote = "double", indent = null} = {}) {
   return string;
 }
 
-function format(value, options) {
-  const string = inspect(value, options);
+function embed(string) {
   const lines = string.split("\n");
   return lines.map((line) => `${PREFIX} ${line}`).join("\n");
 }
 
+function format(value, options) {
+  const string = inspect(value, options);
+  return embed(string);
+}
+
 export function createRuntime(initialCode) {
   let code = initialCode;
   let prevCode = null;
@@ -71,10 +75,15 @@ export function createRuntime(initialCode) {
     for (const node of nodes) {
       const start = node.start;
       const {values} = node.state;
-      if (values.length) {
-        const output = values.map(({value, options}) => format(value, options)).join("\n") + "\n";
-        changes.push({from: start, insert: output});
+      const groupValues = groups(values, (v) => v.options?.key);
+      let output = "";
+      for (let i = 0; i < groupValues.length; i++) {
+        const [key, values] = groupValues[i];
+        const f = values.map(({value, options}) => inspect(value, options));
+        output += key === undefined ? f : key + ": " + f;
+        output += i === groupValues.length - 1 ? "" : "\n";
       }
+      if (output) changes.push({from: start, insert: embed(output) + "\n"});
     }
 
     dispatch(changes);

test/js/echo-key.js

@@ -0,0 +1,18 @@
+export const echoKey = `binarySearch('g', ["a", "b", "c", "d"], echo);
+
+function binarySearch(key, array, echo=() => {}) {
+  let lo = 0;
+  let hi = array.length - 1;
+  while (lo <= hi) {
+    const mi = Math.floor((lo + hi) / 2);
+    const val = array[mi];
+    echo(lo, {key: "lo"});
+    echo(hi, {key: "hi"});
+    echo(mi, {key: "mi"});
+    echo(val, {key: "val"});
+    if (val < key) lo = mi + 1;
+    else if (val > key) hi = mi - 1;
+    else return mi;
+  }
+  return -1;
+}`;

test/js/index.js

@@ -14,3 +14,4 @@ export {mandelbrotSet} from "./mandelbrot-set.js";
 export {matrixRain} from "./matrix-rain.js";
 export {jsDocString} from "./js-doc-string.js";
 export {commentLink} from "./comment-link.js";
+export {echoKey} from "./echo-key.js";