Add zip command

src/vm/commands/index.ts

@@ -45,6 +45,7 @@ import {Drop} from "./drop.js";
 import {Sort} from "./sort.js";
 import {Set} from "./set.js";
 import {Assign} from "./assign.js";
+import {Zip} from "./zip.js";
 
 export type Commands = Command<CommandData>[]
 export const commands: Commands = [
@@ -94,4 +95,5 @@ export const commands: Commands = [
     new Upper,
     new Word,
     new Words,
+    new Zip,
 ]

src/vm/commands/zip.ts

@@ -0,0 +1,38 @@
+import {Command, ParseContext, StrDestructured, StrTerm} from "./command.js";
+import {Awaitable} from "../../util/types.js";
+import {LexInput} from "../lexer.js";
+import {StrVM} from "../vm.js";
+
+export type ZipData = {
+	with: StrTerm,
+}
+
+export class Zip extends Command<ZipData> {
+	attemptParse(context: ParseContext): Awaitable<ZipData> {
+		return {
+			with: context.popTerm(),
+		}
+	}
+
+	getDisplayName(): string {
+		return 'zip'
+	}
+
+	isParseCandidate(token: LexInput): boolean {
+		return this.isKeyword(token, 'zip')
+	}
+
+	execute(vm: StrVM, data: ZipData): Awaitable<StrVM> {
+		return vm.replaceContextMatchingTerm(ctx => ({
+			destructured: lhs => {
+				const rhs = ctx.resolveDestructured(data.with)
+				const zipped: StrDestructured['value'] = []
+				for ( let i = 0; i < Math.max(lhs.length, rhs.length); i += 1 ) {
+					if ( lhs[i] ) zipped.push(lhs[i])
+					if ( rhs[i] ) zipped.push(rhs[i])
+				}
+				return zipped
+			},
+		}))
+	}
+}

src/vm/vm.ts

@@ -266,6 +266,10 @@ export class ExecutionContext {
         return unwrapString(this.resolveRequired(term))
     }
 
+    resolveDestructured(term: StrTerm) {
+        return unwrapDestructured(this.resolveRequired(term))
+    }
+
     resolveInt(term: StrTerm): number {
         return unwrapInt(this.resolveRequired(term))
     }