The year was 1936. A 33-year old mathematician, Alonzo Church, published his research on the foundations of mathematics. In doing so, he created the so-called lambda calculus, which was a model for the recently created field of computation. In collaboration with Alan Turing, he would then go on to prove that the lambda calculus is equivalent to a Turing machine. The relevance of this discovery is fundamental to programming—it means that we can write any program for a modern computer by using lambdas and by taking advantage of lambda calculus. That explains why it's called lambda—mathematicians have long preferred single Greek letters for every notation. But what exactly is it?
If you ignore all the mathematical notations, a lambda is just a pure function that can be applied to variables or values. Let's take a look at an example. We will...