Replace StringRange w/ an actual StrRVal + more command implementations

src/vm/commands/contains.ts

@@ -1,5 +1,5 @@
 import { LexInput } from "../lexer.js";
-import {Command, ParseContext, StrTerm, unwrapString} from "./command.js";
+import {Command, ParseContext, StrTerm, unwrapString, wrapString} from "./command.js";
 import {StrVM} from "../vm.js";
 import {Awaitable} from "../../util/types.js";
 
@@ -19,9 +19,10 @@ export class Contains extends Command<{ find: StrTerm }> {
     }
 
     execute(vm: StrVM, data: { find: StrTerm }): Awaitable<StrVM> {
-        return vm.inPlace(ctx =>
-            ctx.replaceSubject(sub =>
-                sub.emptyUnlessCondition(s =>
-                    s.includes(ctx.resolveString(data.find)))))
+        return vm.tapInPlace(ctx =>
+            ctx.replaceSubjectAsString(sub =>
+                sub.includes(ctx.resolveString(data.find))
+                    ? sub
+                    : ''))
     }
 }