str/src/vm/commands/join.ts

import {Command, joinDestructured, ParseContext, StrTerm, unwrapDestructured, wrapString} from "./command.js";
import {LexInput} from "../lexer.js";
import {StrVM} from "../vm.js";
import {Awaitable} from "../../util/types.js";

export class Join extends Command<{ with?: StrTerm }> {
    attemptParse(context: ParseContext): { with?: StrTerm } {
        return {
            with: context.popOptionalTerm(),
        }
    }

    getDisplayName(): string {
        return 'join'
    }

    isParseCandidate(token: LexInput): boolean {
        return this.isKeyword(token, 'join')
    }

    execute(vm: StrVM, data: { with?: StrTerm }): Awaitable<StrVM> {
        return vm.tapInPlace(ctx =>
            ctx.replaceSubject(sub => {
                if ( data.with ) {
                    return wrapString(
                        unwrapDestructured(sub)
                            .map(part => part.value)
                            .join(ctx.resolveString(data.with)))
                }

                return wrapString(joinDestructured(unwrapDestructured(sub)))
            }))
    }
}