Editing 1270: Functional

{{comic
| number    = 1270
| date      = September 26, 2013
| title     = Functional
| image     = functional.png
| titletext = Functional programming combines the flexibility and power of abstract mathematics with the intuitive clarity of abstract mathematics.
}}

==Explanation==
{{incomplete|1270: Functional}}

[[White Hat]] questions [[Cueball]]'s faith in {{w|functional programming}}. [[Cueball]] responds saying, "Tail recursion is its own reward."

Functional programming is a famous method in modern programs. Unlike {{w|Procedural programming|procedures}} they always return a value, like {{w|Sine|sine(x)}} returns 1 when x is 90. Furthermore the function even can call itself, starting a loop. This is called {{w|Recursion (computer science)|recursion}}, each call does allocate it's own memory ({{w|Call stack|stack}}), and works independently to the other calls. 

The main difference between functional programming and {{w|imperative programming}} is that in imperative programmings the functions do have a {{w|control flow}} or local variables. In order to {{w|Iteration|iterate}} they usually use {{w|Loop (programming)|loops}}.

For example, the {{w|factorial}} function can be coded imperatively as:

 factorial(n):
     prod = 1
     while n > 0:
         prod = prod * n
         n = n - 1
     end
     return prod

A recursive (and functional) definition can look like this:

 factorial(n) = 
     if n > 0
         n * factorial(n-1)
     else
         return 1

In this situation, the recursion stops when the argument (n) is not greater than zero. Without the conditional definition it would be an infinite loop. The {{w|Tail recursion}} is a special case of recursion whose very '''last''' operation is to invoke the function itself or return a definite value.

This example is tail recursive inside the helper function, which should not work because the return statement is missing:

 factorial(n) = factorial_helper(n, 1)
 
 factorial_helper(n, prod) = 
     if n > 0 
         factorial_helper(n - 1, prod * n)
     else
         prod

In functional programming tail recursion is detected by the compiler or interpreter and can be executed as efficient as loops in imperative programming languages. This makes tail recursion an essential programming technique in functional programming.

Cueball is making a play on words where "Tail recursion is its own reward" is used both in the "it's worth doing on elegance and intellectually satisfying grounds alone" sense and in the sense that "the 'tail call' of a function is its final step, and is the final step (and hence the result/reward) for <em>all levels</em> of a tail-recursive function".

The title text says that to {{w|Abstract mathematics|abstract mathematicians}} functional programming is both powerful and flexible, as well as intuitive and clear since it comes very close to the way mathematicians usually describe functions. The humorous contrast is that to non-mathematicians, functional programming can be exactly the opposite (thus being non-intuitive and unclear as abstract mathematics appears to them). And it's also a reference to a common saying about the imperative programming language, 'C': "C combines the flexibility and power of {{w|assembly language}} with the user-friendliness of assembly language".

==Transcript==
:[White Hat stands behind Cueball, who is sitting at a computer]
:White Hat: Why do you like functional programming so much? What does it actually ''get'' you?
:Cueball: Tail recursion is its own reward.

{{comic discussion}}
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Cueball]]
[[Category:Programming]]
[[Category:Recursion]]