What obvious way of using Vavr's fold() am I missing here?

StringBuilderWithFolding.java

private String linesOf(List<String> lines) {
    StringBuilder stringBuilder = new StringBuilder();
    lines.map(line -> stringBuilder.append(line).append(System.lineSeparator()));
    return stringBuilder.toString();
}

Aha! So that differentiates "fold left" from "fold". I think I understand. Thank you.

@jovaneyck Much better, thanks!

package ca.jbrains.pos.test;

import io.vavr.collection.LinearSeq;

public class LineBuilder {

    private final StringBuilder stringBuilder = new StringBuilder();

    public static String linesOf(LinearSeq<String> lines) {
        return lines.foldLeft(new LineBuilder(), LineBuilder::appendAsALine).toString();
    }

    public LineBuilder appendAsALine(String line) {
        this.stringBuilder.append(line).append(System.lineSeparator());
        return this;
    }

    @Override
    public String toString() {
        return stringBuilder.toString();
    }
}