Stub out story/controls and use code-mirror with vim for text-editing

src/ui/REPL.tsx

@@ -7,6 +7,7 @@ import { SourceText, sourceText } from 'src/lang/parser/source_text';
 import { ParseError, parseExpr } from 'src/lang/parser/parser';
 import { ShowParseError } from './ParseError';
 import { Val } from './Value';
+import { CodeEditor } from './CodeEditor';
 
 namespace ReplResult {
   export type Idle =
@@ -55,25 +56,15 @@ export function ExprREPL() {
 
   return (
     <section>
-      <textarea
-        placeholder="+(3, 4)"
-        rows="5"
-        value={input()}
-        onInput={(e) => setInput(e.currentTarget.value)}
-        onKeyDown={(e) => {
-          // Check for Enter + (Ctrl or Command for Mac)
-          if (e.key === "Enter" && (e.ctrlKey || e.metaKey)) {
-            e.preventDefault(); // Stop the newline from being added
-            runExecution();
-          }
-        }}
+      <CodeEditor 
+        value={input()} 
+        onUpdate={setInput} 
+        onRun={runExecution} 
       />
 
       <button onClick={runExecution}>Run</button>
-
-      <hr />
       
-      <div>
+      <div style={{ "margin-top": "1rem" }}>
         <Switch>
           <Match when={result().tag === "idle"}>
             { "" }