Implement group command + fallback error handling for invalid tables in output

src/vm/commands/group.ts

@@ -0,0 +1,56 @@
+import {LexInput} from "../lexer.js";
+import {Command, hashStrRVal, ParseContext, StrRVal, StrTerm, wrapDestructured} from "./command.js";
+import {StrVM} from "../vm.js";
+import {Call} from "./call.js";
+
+type GroupData = {
+	callable: StrTerm,
+}
+
+export class Group extends Command<GroupData> {
+	async attemptParse(context: ParseContext): Promise<GroupData> {
+		return {
+			callable: await context.popTerm(),
+		}
+	}
+
+	isParseCandidate(token: LexInput): boolean {
+		return this.isKeyword(token, 'group')
+	}
+
+	getDisplayName(): string {
+		return 'group'
+	}
+
+	async execute(vm: StrVM, data: GroupData): Promise<StrVM> {
+		return vm.replaceContextMatchingTerm(ctx => ({
+			destructured: async sub => {
+				const callable = ctx.resolveLambda(data.callable)
+				const groups: Record<string, StrRVal[]> = {}
+
+				for ( const part of sub ) {
+					// Run the exec in a child VM and group on the hashed result:
+					await vm.runInChild(async (childVM, childCtx) => {
+						await childCtx.replaceSubjectMatchingTerm({ override: part.value })
+
+						await (new Call).execute(childVM, {
+							callable,
+							params: [],
+						})
+
+						const groupVal = hashStrRVal(childCtx.getSubject())
+						groups[groupVal] ??= []
+						groups[groupVal].push(part.value)
+					})
+				}
+
+				const groupValues = Object.values(groups)
+					.map(group =>
+						wrapDestructured(
+							group.map(value => ({ value }))))
+
+				return groupValues.map(value => ({ value }))
+			},
+		}))
+	}
+}

src/vm/commands/index.ts

@@ -52,6 +52,7 @@ import {Call} from "./call.js";
 import {Chunk} from "./chunk.js";
 import {Script} from "./script.js";
 import {Take} from "./take.js";
+import {Group} from "./group.js";
 
 export type Commands = Command<CommandData>[]
 export const commands: Commands = [
@@ -68,6 +69,7 @@ export const commands: Commands = [
     new Enclose,
     new Exit,
     new From,
+    new Group,
     new Help,
     new History,
     new Indent,