fix #79; R (Rscript) data loaders

Author: mbostock

docs/data-loaders.html

@@ -10,7 +10,7 @@
     **Data loaders** are special cells that run "ahead" at build time via an interpreter, rather than "live" when you view a notebook in the browser. Data loaders are useful for preparing static data, ensuring consistency and stability, and improving performance. Think of data loaders as a generalization of [database connectors](./databases) that allow languages besides SQL.
   </script>
   <script id="7" type="text/markdown">
-    Notebooks currently support Node.js and Python data loaders. We will likely add additional interpreters in the future.
+    Notebooks currently support Node.js, Python, and R data loaders. We will likely add additional interpreters in the future.
   </script>
   <script id="3" type="text/markdown">
     As an example, here is a trivial Python cell that says hello, and reports the current version of Python:
@@ -144,4 +144,15 @@
   <script id="30" type="text/markdown">
     If you have a virtual environment (`.venv`) in the same directory as the notebook, it will automatically be used. However, packages are not installed implicitly; you must install packages yourself, typically using `pip`. (And we recommend using `pip freeze` to create a `requirements.txt`.)
   </script>
+  <script id="31" type="text/markdown">
+    ## R data loaders
+
+    R data loaders require R to be installed in one of the following locations:
+
+    - `/opt/homebrew/bin/Rscript` (Homebrew)
+    - `/opt/local/bin/Rscript` (MacPorts)
+    - `/Library/Frameworks/R.framework/Resources/bin/Rscript` (official R installer)
+    - `/usr/local/bin/Rscript` (official R installer)
+    - `/usr/bin/Rscript` (operating system)
+  </script>
 </notebook>

docs/observable.tmpl

@@ -115,7 +115,7 @@
             </a>
             <a href="/notebook-kit/data-loaders" style="color: inherit;">
               <div>Data loaders</div>
-              <div style="opacity: 0.8; font-weight: normal; font-size: 14px;">Prepare static data by running Node.js and Python cells</div>
+              <div style="opacity: 0.8; font-weight: normal; font-size: 14px;">Prepare static data by running Node.js, Python, or R</div>
             </a>
             <a href="/notebook-kit/desktop" style="color: inherit;">
               <div>Desktop</div>

src/interpreters/index.ts

@@ -20,6 +20,8 @@ export function getInterpreterCommand(interpreter: string): [command: string, ar
       return ["node", ["--input-type=module-typescript", "--permission", "--allow-fs-read=."]];
     case "python":
       return ["python3", []];
+    case "r":
+      return ["Rscript", ["-"]];
     default:
       throw new Error(`unknown interpreter: ${interpreter}`);
   }

src/lib/interpreters.ts

@@ -1,7 +1,7 @@
 import type {Cell} from "./notebook.js";
 
 export function isInterpreter(mode: Cell["mode"]): boolean {
-  return mode === "node" || mode === "python";
+  return mode === "node" || mode === "python" || mode === "r";
 }
 
 export function getInterpreterExtension(format: Cell["format"]): string {

src/lib/notebook.ts

@@ -39,7 +39,7 @@ export interface CellSpec {
   /** the committed cell value; defaults to empty */
   value?: string;
   /** the mode; affects how the value is evaluated; defaults to js */
-  mode?: "js" | "ts" | "ojs" | "md" | "html" | "tex" | "dot" | "sql" | "node" | "python";
+  mode?: "js" | "ts" | "ojs" | "md" | "html" | "tex" | "dot" | "sql" | "node" | "python" | "r";
   /** if true, the editor will stay open when not focused; defaults to false */
   pinned?: boolean;
   /** if true, implicit display will be suppressed; defaults to false */

src/lib/serialize.ts

@@ -71,6 +71,8 @@ function serializeMode(mode: Cell["mode"]): string {
       return "application/vnd.node.javascript";
     case "python":
       return "text/x-python";
+    case "r":
+      return "text/x-r";
     case "ojs":
       return "application/vnd.observable.javascript";
     case "ts":
@@ -96,6 +98,8 @@ function deserializeMode(mode: string | null): Cell["mode"] {
       return "node";
     case "text/x-python":
       return "python";
+    case "text/x-r":
+      return "r";
     case "application/vnd.observable.javascript":
       return "ojs";
     case "text/x-typescript":