What is a lambda (function)?

Question

For a person without a comp-sci background, what is a lambda in the world of Computer Science?

Answer 1

In Javascript, for example, functions are treated as the same mixed type as everything else (int, string, float, bool). As such, you can create functions on the fly, assign them to things, and call them back later. It's useful but, not something you want to over use or you'll confuse everyone who has to maintain your code after you...

This is some code I was playing with to see how deep this rabbit hole goes:

var x = new Object;
x.thingy = new Array();
x.thingy[0] = function(){ return function(){ return function(){ alert('index 0 pressed'); }; }; }
x.thingy[1] = function(){ return function(){ return function(){ alert('index 1 pressed'); }; }; }
x.thingy[2] = function(){ return function(){ return function(){ alert('index 2 pressed'); }; }; }

for(var i=0 ;i<3; i++)
    x.thingy[i]()()();

Answer 2

You can think of it as an anonymous function - here's some more info: Wikipedia - Anonymous Function

Answer 3

In context of CS a lambda function is an abstract mathematical concept that tackles a problem of symbolic evaluation of mathematical expressions. In that context a lambda function is the same as a lambda term.

But in programming languages it's something different. It's a piece of code that is declared "in place", and that can be passed around as a "first-class citizen". This concept appeared to be useful so that it came into almost all popular modern programming languages (see lambda functions everwhere post).