Introductory Programming
Fall 2004

For next Tuesday you should

1) Work on Homework 5.

2) Read Chapters 6 and 7.


Fruitful functions
------------------

At the end of a function call, the stack frame disappears,
along with the parameters and local variables.

All that's left is

1) any changes the function made, which are called side-effects

2) the return value


The functions you have written so far are "void functions"
because they don't return anything.

Functions that return something are called "fruitful".

You have already _used_ several fruitful functions,
including the math functions.

And you saw some in Amoebas.py:

def make_amoeba(world, color='violet'):
    # make an amoeba with the given color and randomize it
    a = Amoeba(world)
    a.color1 = color
    randomize(a)
    return a

def randomize(a, limit):
    # choose a random location and move the ameoba there
    x = random_coordinate(limit)
    y = random_coordinate(limit)
    teleport(a, x, y)

def random_coordinate(limit):
    # choose a random number between -limit and limit
    r = random.uniform(-limit, limit)
    return r

amy = make_amoeba(world, 'pink')


Exercise: draw a stack diagram for this code.

Exercise: write a function that takes two Amoebas and returns
	  the distance between them.

Exercise: write a function that takes two Amoebas and returns
	  True if the distance between them is less than 1.0,
	  and False otherwise.