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;;   CSU211 Lab 6 - Trees with application in Pathology   ;;
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;; Author: Prof. Kathi Fisler, WPI
;; Edited: Matthias Felleisen

;; SOURCE
;; "Untangling the Roots of Cancer" by W. Wayt Gibbs. 
;; Published in _Scientific American_, July 2003.

#|
Lab Motivation and Goals:
This lab is designed to help you practice
 - programming with trees
 - using the random function
 - representing biological data as a progamming construct
 - using programs to simulate cancer experiments

Background Information:
Although cancer is one of the leading causes of death in the 
United States, research on the subject still has a long way to 
go before any cures might be discovered. Little is known about 
the causes of cancer, but there are several widely accepted 
theories. Previously, scientists believed that after an 
initial mutation into a malignant form, cancer cells 
essentially create  clones of themselves within the tumors as 
they multiply. However, recent research has shown that this may
not be the case. In fact, several studies have revealed that
cancer cells within a tumor are very diverse, with many different
mutations occuring simultaneously.

In this lab, you will use Scheme programs to simulate and
investigate mutations within malignant cancer tumors. You will
need to consider the following six traits that distinguish cancer 
cells from normal cells:
- Growth without "Go" signals (G)
    Normals cells wait for an external message before 
    dividing, but cancer cells often create their 
    own messages, causing them to multiply without 
    external control.
- Growth despite "Stop" commands (S)
    Under normal conditions, if one group of cells becomes 
    too big, its neighbors send messages to stop the division
    of that group. Cancer cells have the ability to ignore 
    these.
- Evasion of built-in autodestruct mechanisms (A)
    In healthy cells, genetic damage can activate a 
    self-destruct mechanism which destroys possibly dangerous
    cells. Without outside intervention, cancer cells can 
    bypass these mechanisms and continue dividing.
- Ability to construct blood vessels (B)
    Since tumors need oxygen and nutrients to survive, some 
    cancer cells have the ability to stimulate construction
    of blood vessels through the growing mass.
- Effective immortality (I)
    Normal cells can only divide approximately 70 times before 
    dying, but since cancer cells need to divide much more 
    than this to form a tumor, they work around systems that
    control reproductive limits.
- Power to invade other tissues and spread to other organs (O)
    Cancer cells have the unique ability to move from one 
    area of the body to another and continue multiplying, 
    which is often life-threatening.

Just like normal cells, each cancerous cell divides into two
new cells. In order to keep track of mutations that occur as 
cancerous cells divide it is helpful to think of tumors as 
their history, a tree, with the original cell at the root. 
This way, it is possible to see how the cells mutate as they 
divide and the point where mutations happen in the big 
picture. To do this, we will use the following data 
definitions: |#

;; A CellGroup is either:
;; -- (make-cell number cancer-quality)
;; -- (make-cell-group cancer-quality CellGroup CellGroup)
(define-struct cell (time cancer-factor))
(define-struct cell-group (cancer-factor div1 div2))

;; A (cancer)Quality is a
;; -- (make-cancer-quality Boolean Boolean Boolean 
;;                         Boolean Boolean Boolean)
(define-struct cancer-quality (G S A B I O))

;; In this definition, time is the time it takes to divide 
;; once, cancer-factor consists of the factors described 
;; above, and div1 and div2 are the results of a cell's 
;; division.
;; ---------------------------------------------------------