[WIP] Start implementing execution in the new TS version

src/vm/commands/enclose.ts

@@ -1,5 +1,7 @@
 import {Command, ParseContext, StrTerm} from "./command.js";
 import {LexInput} from "../lexer.js";
+import {StrVM} from "../vm.js";
+import {Awaitable} from "../../util/types.js";
 
 export type EncloseData = {
     left?: StrTerm,
@@ -21,4 +23,33 @@ export class Enclose extends Command<EncloseData> {
     isParseCandidate(token: LexInput): boolean {
         return this.isKeyword(token, 'enclose')
     }
+
+    execute(vm: StrVM, data: EncloseData): Awaitable<StrVM> {
+        return vm.inPlace(ctx => {
+            const [left, right] = this.determineSurroundingStrings(
+                data.left ? ctx.resolveString(data.left) : undefined,
+                data.right ? ctx.resolveString(data.right) : undefined,
+            )
+
+            return ctx.replaceSubject(sub =>
+                sub.modify(s => `${left}${s}${right}`))
+        })
+    }
+
+    private determineSurroundingStrings(left?: string, right?: string): [string, string] {
+        if ( !left ) {
+            left = '('
+        }
+
+        if ( !right ) {
+            right = ({
+                '(': ')',
+                '[': ']',
+                '{': '}',
+                '<': '>',
+            })[left] ?? left
+        }
+
+        return [left, right]
+    }
 }