Until I started looking at C# 3.0, I had never heard of lambda expressions. A quick glance at Wikipedia tells me that they seem to pre-date computers, and languages like Lisp and Ruby seem to be based on them. But what the heck are lambda expressions?? The short answer is: They are just shorthand anonymous methods.
It took me a little while to get my head wrapped around they syntax (especially the "classical" syntax on wikipedia), but now I get it!! In the simplest possible example, here is a function which adds one to the parameter:
Func<int, int> increment = A => A + 1;Console.WriteLine(increment(5)); // outputs 6
Basically, we are defining a function "increment" as its parameter A, plus one. Ok, that's not so bad, and I know a lot of places I could use a quick little function definition to parse some input or test some conditions. Given that, I thought I would try something a little harder ... factorial.
Now with factorial, I ran into some immediate problems. I don't think that lambda expressions are designed to be recursive. I couldn't find an equivalent to "this" for the expression, and if I reference the function itself, I get an error telling me that I am using an undefined variable. After some tinkering, I found a way around this. Lambda expressions can be passed as parameters to other lambda expressions. So what if I just passed my factorial expression a reference to itself.
Func<long, object, long> f = (A, B) => A == 0 ? 1 : (A*((Func<long,object,long>)B)(A-1,B));Func<long, long> factorial = A => f(A, f);
Console.WriteLine(factorial(25).ToString("#,###")); // outputs 7,034,535,277,573,963,776
And so that's what I did. I had to pass the function reference as an object because I could not really specify its type. f's definition would look like this if I tried:
Func<long, Func<long, Func<long, ... and so on ... , long>, long>, long>
The "f" expression does the real factorial work, "factorial" just gets the first iteration going. Are lambda expressions going to change the way we program?? I don't know. What do you think?
Lisp and similar languages (which are) seem to be making a comeback, and I had no clue that Orbitz.com is written in Lisp until I read it on wikipedia. I don't really know anything about Lisp, but it got me thinking that maybe Lisp could be a first class .NET language now that lambda expressions will be baked into the CLR 3.0. I'll have to look into this further.