.Open CS320 Lab 13 LISP Laboratory Number 3
. Check out New things on the Course Web Page
.See http://www.csci.csusb.edu/dick/cs320/
. Goal
This lab should teach you how to create and use
new functions that manipulate lists.
You should record your insights and confusions
in a new cs320 lab page and link it to you home/index page.

Let me know by
calling me across to your workstation when done.
To earn full credit the work must be done before the end of the lab and 
should contain a list of at least a note.  The note is a short paragraph
with one or two
sentences, a new LISP function, and a description of what it does.
. Required Work
Use a text editor and the XLISP system to develop
a working solution in LISP to one of the problems
set in the class today.
. Deliverables
An addition to your web site with links to a couple
of functions from the problems at the end of Chapter 15 of Sebesta
that we covered in class.  Add what you have learned by coding and debugging them.
. Resources
.Set
	Keep your handout on LISP open beside you and look in it for
the rules of LISP.
	Use the online resources:
.See http://www/dick/cs320/lab/12.html
.See http://www/dick/cs320/lab/13.html
.See http://www/dick/samples/lisp.html
.See http://www/dick/cs320/lisp.functions.html
.See http://www/dick/cs320/lisp/functions.lsp
	Open many windows and use your hilight-and-paste feature to save time.
.Close.Set
. Hints
.Set
	Forget about efficiency.  
	Let the user run functions that help them solve problems. No User Interfaces!
	Remember that all data in LISP are lists and all programs are functions.
	Divide and Conquer:
.List
	Break up the given problems into smaller problems, top-down.
	Solve each problem, bottom-up, as a function that:
.Box
	Divides:
.Set
	the data into `special cases` and solves each one,
Example: a COND with cases for NIL, Atoms, from Cons
	the data into `pieces`, work on each piece in turn,
Example: do something to the CAR and then to the CDR,
	a complex function into a composition of smaller functions,
Example: To sum square the sum of a list: define a square function (sq n) and
a sum function(adder L) and then (define (sqsum L) (sq (sum l)))
.Close.Set
	and then assembles the results of solving the parts of the problem.
.Close.Box
	The code's structure reflects how you divide up the problem.
.Close.List

	Be very very careful about counting parentheses.
	'vi' can help you track parentheses if you do the following in 'vi'
.As_is 		:set showmatch

	Use an editor to write your functions and their test cases then either
.Set
	Copy and paste into a window running XLisp to run them...
	or
	Save the version ( :w in vi) and run xlisp on it. (:!xlisp % in vi)
.Close.Set
.Close.Box

. Review -- Displaying the structure of a LISP value
LISP data is stored in what is called a binary tree:  each item
of data is a "leaf"(an atom), empty (NIL) or a pair (car . cdr).
We call the car and cdr of a pair the branches:
.As_is 		((1   .   2) . 3)
The data looks like this (with a 'o' replacing the '.').
.As_is 		    o
.As_is 		   / \
.As_is 		  o   3
.As_is 		 / \
.As_is 		1   2
.Net
	tree::= NIL | leaf | pair,
	pair::= (car . cdr),
	leaf::=atom,
	car::=tree,
	cdr::=tree.
.Close.Net

Down load/Save this file as text:
.See http://www/dick/cs320/lisp/show.lsp

Use this UNIX command to look inside the file:
.As_is 			cat show.lsp

Run this UNIX command in a terminal window:
.As_is 			xlisp show.lsp


Inside the running XLISP try these command:
.As_is 			SHOW
.As_is 			(show '(a b))
.As_is 			(show '(a b c))
.As_is 			(show '(a b c d))
.As_is 			(show '((a b)(c d)))
	
This function (or something like it) is a handy
tool when you want to see the structure of a complex
list structure.... for example the value `show` itself.
.As_is			(show show)


. To Leave LISP
To exit lisp, input the EOT character CTRL/D
.Close CS320 Lab 13 LISP Laboratory Number 3
. Dirty LISP
It is possible to write LISP code that is full of
loops and the equivalent of {...} and assignments.
The key operators are: PROG, PROGN, DO, DO*,...

You should resist the temptation to use these since
your task is to learn functional thinking... which
avoids these concepts.

In more advanced classes you may use (LET ....) and (LET* ....)
to avoid an intermediate function.
. Check the Preparation for next class
.See ../14.html
. Want to learn more LISP?
Here you can develop a game, expression by expression
.See http://www.lisperati.com/
( when I tried this I had to define at least one extra
function: (defun push (item place) (setf place (cons item place)))
)
or follow the links on my
.See ../../samples/lisp.html
page.