[WIP] Implement save, load, over, infile, outfile, on, lipsum, help + start implementing undo, redo, exit, edit

src/vm/commands/over.ts

@@ -1,6 +1,7 @@
 import {Command, CommandData, ParseContext, StrLVal} from "./command.js";
 import {Executable} from "../parse.js";
 import {LexInput} from "../lexer.js";
+import {StrVM} from "../vm.js";
 
 export type OverData = {
     subject: StrLVal,
@@ -22,4 +23,18 @@ export class Over extends Command<OverData> {
     isParseCandidate(token: LexInput): boolean {
         return this.isKeyword(token, 'over')
     }
+
+    async execute(vm: StrVM, data: OverData): Promise<StrVM> {
+        return vm.tapInPlace(async parentCtx => {
+            const oldValue = parentCtx.resolveRequired(data.subject)
+            const newValue = await vm.runInChild(async (child, childCtx) => {
+                await childCtx.replaceSubject(() => oldValue)
+                await data.exec.command.execute(child, data.exec.data)
+                return childCtx.getSubject()
+            })
+
+            parentCtx.inScope(scope =>
+                scope.setOrShadowValue(data.subject, newValue))
+        })
+    }
 }