Some functions return plain values. Other functions return fancy values with the plain values inside. There are different types of fanciness. One simple kind i

Some functions return plain values. Other functions return fancy values with the plain values inside. There are different types of fanciness. One simple kind is called option. An option may have a plain value inside it or it may be nothing. Imagine looking up a phone number in the phone book. You get the name wrapped in an option or nothing because the person is not listed. Another fancy kind of thing is a Future. It runs some operation like looking up something in a database. When you call the function it just returns this fancy thing and at some point the database sends a response and that response is a plain value inside it. If you want the plain value you have to wait for the future. Well quite often you have functions that return fancy things and you would like to chain them together; lookup some user and then lookup their account. Instead of waiting for the first one and getting the plain value out then passing that to the second one and waiting for that, you could write some code that chained the two functions together for you. That composing of functions that return fancy things is called join or flatmap. If you also have a function that can put any value into a fancy thing (this is called unit or pure) you now have what is called a monad.