Functional programming

Function Libraries:
	- libstg example
	- Interfaces are commonly defined by functions
		 Example:  math library
		 Example:  POSIX
	- It is possible to write functions in C and use them in Python
		Maybe I'll show you someday...	
	
Recursion, part #1:
	- We'll talk more about recursion near the end of the course
	- A function can call itself for productive purposes
	- Factorial example...but there will be another example later today

First-Class Functions:
	- A function is a value, like a number or a string
	- A language has first-class functions if you can:
		+ Pass a function to a function
		+ Return a function from a function
		+ Create a function with no name (anonymous function)
	- Demos...
	- Python mostly has first-class functions (no statements in anonymous functions)
	- This brings up some issues!
		+ Closures

Why does this look so natural in Python?
	- Let's look at it in C for a minute
	- Operating systems are written in C
	- They're full of function pointers!

Java and first class functions:
	- No
	- You can sort of hack it with an object and methods...
	- May have changed in Java 8

A natural question:  Is this useful?
	- Example:  graphalign 
	- There aren't any programs you can't write without them
	- Passing functions to functions is used for a lot of things
		+ Example:  start_new_thread
	- I didn't see it mentioned in the book
	- But I use first-class functions regularly!

Ok, let's play recursion!
	- With the turtle!
	- How do you draw concentric circles?