Functional languages are as old as programming is, and even older. Although functional languages have been considered for decades exotic and cumbersome, in recent years, mainstream programming languages such as Java, C# and Python included functional stuff such as lambdas, closures etc. In this talk I'll show how to implement from scratch a simple functional language, drawing inspiration from some classic papers by PJ Landin. These papers are jewels through which shine the basic ideas filtered in modern languages, from Javascript to Clojure, and they are worth reading still today.