Introduce TermOperator helper and refactor execute()s to use replaceSubjectMatchingTerm

src/vm/commands/unique.ts

@@ -17,20 +17,19 @@ export class Unique extends Command<{}> {
     }
 
     execute(vm: StrVM): Awaitable<StrVM> {
-        return vm.tapInPlace(ctx =>
-            ctx.replaceSubject(sub => {
+        return vm.replaceContextMatchingTerm({
+            destructured: sub => {
                 const seen: Record<string, boolean> = {}
-                return wrapDestructured(
-                    unwrapDestructured(sub)
-                        .filter(part => {
-                            const hash = hashStrRVal(wrapString(part.value))
-                            if ( seen[hash] ) {
-                                return false
-                            }
+                return sub.filter(part => {
+                    const hash = hashStrRVal(wrapString(part.value))
+                    if ( seen[hash] ) {
+                        return false
+                    }
 
-                            seen[hash] = true
-                            return true
-                        }))
-            }))
+                    seen[hash] = true
+                    return true
+                })
+            },
+        })
     }
 }