[WIP] Start implementing execution in the new TS version

src/vm/commands/contains.ts

@@ -1,5 +1,7 @@
 import { LexInput } from "../lexer.js";
-import {Command, ParseContext, StrTerm} from "./command.js";
+import {Command, ParseContext, StrTerm, unwrapString} from "./command.js";
+import {StrVM} from "../vm.js";
+import {Awaitable} from "../../util/types.js";
 
 export class Contains extends Command<{ find: StrTerm }> {
     attemptParse(context: ParseContext): { find: StrTerm } {
@@ -15,4 +17,11 @@ export class Contains extends Command<{ find: StrTerm }> {
     isParseCandidate(token: LexInput): boolean {
         return this.isKeyword(token, 'contains')
     }
+
+    execute(vm: StrVM, data: { find: StrTerm }): Awaitable<StrVM> {
+        return vm.inPlace(ctx =>
+            ctx.replaceSubject(sub =>
+                sub.emptyUnlessCondition(s =>
+                    s.includes(ctx.resolveString(data.find)))))
+    }
 }