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TUTORIAL 3CSCI3230 (2014-2015 First Term)

By Leo LIU (pfl@cse.cuhk.edu.hk)

Paco WONG (pkwong@cse.cuhk.edu.hk)

CAO Qin (qcao@cse.cuhk.edu.hk)

Hands on Lab@SHB924

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Outline• Lispbox

• Setup• IDE• Example

• Short Review• Guided Practice • Programming Exercises

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Lispbox

1. Download from http://common-lisp.net/project/lispbox/

2. Open Lispbox

Messages and instructions

User input and interpreter output

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Hello World

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LISP IDE• A prompt for you to enter a LISP expression when CL

started: CL-USER>

• REPL: Read-evaluate-print loop• Interactive: at any time you can try your expressions

CL-USER> (cos (/ pi 4))0.7071067811865476D0CL-USER> "hello world""hello world"CL-USER>

Read

EvaluatePrint

Q: How is s-expression evaluated? [See Tutorial 1: Control the Flow of

Evaluation]

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How to Edit, Save, Load and Compile• Edit

• Emacs from Lispbox (Ctrl-h t for a tutorial)• Any other text editors

• Save e.g., testing.lisp (or .cl)• Load (load "testing.lisp")• Compile (compile-file "testing.lisp")

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Example 1mysum.lisp(defun mysum (x y)

;"Sum any two numbers after printing a message.";printf("Summing %d and %d.\n", x, y)

(format t "Summing ~d and ~d.~%" x y)(+ x y))

Lisp IDE> (load “mysum.lisp") ;Load the mysum.lisp to the environment#P"d:/Software/lispbox-0.7/mysum.lisp"> (mysum 10 2) ;Test your functionSumming 10 and 2.12

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Example 2testing.lisp(defun sum_square (n)

(let ((r 0))(do ((i 1 (+ i 1)))

((= i n) r)(setq r (+ r (* i i))))))

Lisp IDE> (load "testing.lisp") ;Load the testing.lisp to the environment#P"d:/Software/lispbox-0.7/testing.lisp"> (sum_square 10) ;Test your function285

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Try (sum_square)Click 3 to kill OR

Press key 3 to abort OR

Press key a to abort

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Emacs• Split the buffer to two vertical frames

• Ctrl-X 3

• Open a file in a buffer• Click the open button OR• Ctrl-X f

• Enable Parentheses Match Highlighting• Save the buffer

• Click the save button

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SLIME• The Superior Lisp Interaction Mode for Emacs

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REVIEW

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Atom• The most basic (indivisible) unit in LISP

• Any combination of characters, except "(" and ")", can be an atom. For an atom with " "(whitespace) character, it needs to be written as |an atom is here|.

• 3 types of Atom:• Symbols

• Not case sensitive.

• E.g. John, abc, 23-Jordan

• Numbers• E.g. 123, 0

• 3/4 ; rational number

• #C(3 4) ; complex number = 3 + 4j

• #C(3/4 4) ; complex number = 0.75 + 4j != 3/4 + 4j

• Constants (self-evaluating)• Symbols that have special meaning

• E.g. NIL, T;Comment here

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List• A non-atomic s-expression.• A collection of atom or list enclosed by parentheses ( ).• (Jordan 23) ; a list of atoms "Jordan" and "23"• (Jordan (3/4 23)) ; a list of atoms Jordan and a list of

"3/4" and "23"• ( ) ; a null list

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Symbolic-Expression• An s-expression is defined recursively:

1. An atom is an s-expression

2. If s1, s2, …, sn are s-expressions, then so is the list (s1 s2 … sn).

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NIL and T• NIL• An special list called the null (empty) list ( )• Also an atom• Means "false" or "nothing"• ANY non-"NIL" symbol is considered as "true" in LISP• A subtype of everything

• T• Reserved as the default symbol for "true".• ALL the data types are subtypes of T.

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Form• A form is an s-expression that is intended to be evaluated.• If it is a list, the first element is treated as the operator

(functions, macros or special forms) and the subsequent elements are evaluated to obtain the function arguments.

Example 1

(+ 2 4)

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Many Functions• S-expression

• Atom and list

• Evaluation and its control• Form, QUOTE and EVAL

• Binding variable explicitly• SET, SETQ and SETF

• Cons cell and list• CONS, CAR, CDR, NTHCDR,

NTH, APPEND, …

• Predicates• TYPEP, SUBTYPEP, EQL, …

• Conditional constructs• IF THEN ELSE, COND, …

• Iteration• LOOP, DO, …

• Let• Function

• DEFUN

• Macro• DEFMACRO

• Structure• DEFSTRUCT

• Property list• GETRefer to the previous tutorials for details

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GUIDED PRACTICE1. If-then-else

2. Recursion 1

3. Recursion 2

4. Prime Test

5. Tree Traversal

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1. If-then-else

(defun isZero (n)

(if (= n 0)

(format t "~D is zero.~%" n)

(format t "~D is not zero.~%" n)))

Try this(isZero 1)(isZero 0)

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2. Recursion 1

;To demonstrate recursion: 1+2+3+4+...+n

(defun sum1 (n)

(if (< n 1)

0

(if (= n 1)

1

(+ (sum1 (- n 1)) n))))

Try this(sum 5)(sum 10)(sum -5)

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3. Recursion 2

;To demonstrate recursion - 1^3+2^3+3^3+4^3+...+n^3

(defun sum3 (n)

(if (< n 1)

0

(if (= n 1)

1

) ) )<Put your code here>

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4. Is Prime ?

Try this(isPrime 1)(isPrime 11)(isPrime -5)

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5. Tree Traversal ;print the tree in order

(defun printTree (tree)

(let ((num (car tree))

(ltree (eval (cadr tree)))

(rtree (eval (caddr tree))))

(if (not tree)

nil

(progn

(print num)(printTree ltree)

(printTree rtree)

))

num))

Try this(printTree '(1 nil nil))(printTree '(2 '(1 nil nil) nil))(printTree '(2 '(1 nil nil) '(3 nil nil)))

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PROGRAMMING EX1. Define a function

2. Define a recursive function and iterative function

3. Read a segment from a list

4. Remove a segment from a list

5. Sort a list

6. Traverse a tree

7. Use program as data

8. Propose an interesting question for yourself!

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Programming Exercise 1• Define a function sum(n) which returns the result of

1+2+3+4+5+6+…+n

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Programming Exercise 2• Define a recursive function Fibonacci_r(n) which returns

the nth number in the Fibonacci sequence.• (Fibonacci_r 1) gives 1• (Fibonacci_r 2) gives 1• (Fibonacci_r 3) gives 2• (Fibonacci_r 4) gives 3• Similarly, define an iterative function Fibonacci_i(n)• Finally, execute (mapcar #'Fibonacci_r '(1 2 3 4 5))

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Programming Exercise 3• Write a function Extract (L i j) which extracts the ith to jth

elements.• (Extract '(1 2 3 4 5) 1 2) gives (2 3)• (Extract '(1 2 3 4 5) 1 1) gives 2• (Extract '(1 2 3 4 5) 0 4) gives (1 2 3 4 5)• (Extract '(1 2 3 4 5) 0 5) gives (1 2 3 4 5)• (Extract '(1 2 3 4 5) 5 6) gives NIL

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Programming Exercise 4• Given a list of length n, we want to remove the cons cells

from j to j+1, where j is from 0 to n-1. Define Splice (L i j) for the purpose.

• (Splice '(1 2 3 4 5) 1 2) gives (1 4 5)• (Splice '(1 2 3 4 5) 1 1) gives (1 3 4 5)• (Splice '(1 2 3 4 5) 0 4) gives NIL• (Splice '(1 2 3 4 5) 0 5) gives NIL• (Splice '(1 2 3 4 5) 5 6) gives (1 2 3 4 5)

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Programming Exercise 5• Write a merge sort function for a list of number.

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Programming Exercise 6• Define a function called tree_all(T) , T is a binary tree as

described in the tutorial, tree_all will return a list (A1,A2,A3,A4), which

• A1 is the largest node of T’s left sub tree• A2 is the smallest node of T’s left sub tree• A3 is the largest node of T’s right sub tree• A4 is the smallest node of T’s right sub tree• Example• >(tree_all '(10 '(38 nil nil) '(20 nil '(11 nil nil))• (38 38 20 11)• >(tree_all '(1 '(10 '(2 nil nil) '(3 nil nil)) '(320 '(24 nil nil) '(95 nil nil) ))• (10 2 320 24)

(* (+ (2) (3)) (- (7) (8)))

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Programming Exercise 7• Define a macro called run_prog(p x) which returns the

value of (p x).• Example• > (run_prog '(+ x 2) 2)• 4• > (run_prog '(+ x (- x 2)) 2)• 2

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Hints

1. Simplify testing.lisp

2. http://www.cs.sfu.ca/CourseCentral/310/pwfong/Lisp/1/tutorial1.html

3. Use do, nthcdr

4. Read next slide

5. http://en.literateprograms.org/Merge_sort_%28Lisp%29

6. Use car, cdr, numberp and define a recursive function

7. Choose among let, lambda, eval, quote and list

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HintsHints for Q4> (setq l '(1 2 3 4 5 6 7 8 9 10 11 12))(1 2 3 4 5 6 7 8 9 10 11 12)> (nthcdr 3 l)(4 5 6 7 8 9 10 11 12)> (nthcdr 3 l)(4 5 6 7 8 9 10 11 12)> (setf (cdr (nthcdr 3 l)) (nthcdr 6 l)) ;because clisp doesn't allow setf on nthcdr(7 8 9 10 11 12)> l(1 2 3 4 7 8 9 10 11 12)

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Suggested Readings• Common Lisp the Language, 2nd Edition

• http://www.cs.cmu.edu/Groups/AI/html/cltl/cltl2.html

• http://lib.store.yahoo.net/lib/paulgraham/onlisp.pdf• Common LISP Hints

• http://www.carfield.com.hk/document/languages/common-lisp-tutorial.html