Here's your version translated to C#: xs.Aggregate("", (prev, cur) => { if (prev != "a" && cur != "a") parseLine(cur); return cur; }); Working demo: https

Here's your version translated to C#: xs.Aggregate("", (prev, cur) => { if (prev != "a" && cur != "a") parseLine(cur); return cur; }); Working demo: https://repl.it/EwaE https://repl.it/EwaE