Lisp:CaseStudy
ref:Lisp(3rd Ed)Winston&Horn(Chapter6)
Donald F. Ross
Lisp:CaseStudy
• title / author / class
collection: library
(attributes)
• data abstraction
• constructor
• reader
• writer
• Program “clichés”
(make)
(get)
(set)
(patterns)
(sound familiar?)
PS - Lisp Case study
• object: book
28/03/2017
• Exercise – build a library system
2
(defun book‐title (book) (defun book‐author (book)
(defun book‐class (book) (defun fictionp
(book) (second (assoc 'title book)) ) (second (assoc 'author book)) )
(second (assoc 'class book)) ) (member 'fiction (book‐class book)) ) (mapcar #’<function> books) (remove‐if #’<predicate> books)
(find‐if
#’<predicate> books)
(count‐if #’<predicate> books)
; apply <function> to each element
; filter
; find first
; count
PS - Lisp Case study
(defun make‐book (title author class)
(defun baw (book author)
(list (list 'title title) (if (eql 'author (first (first book)))
(list 'author author) (cons (list 'author author) (rest book))
(list 'class class) )) (cons (first book) (baw (rest book) author)))))
28/03/2017
Lisp:CaseStudy:theanswer!
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Lisp:CaseStudy:Comments
A
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e
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• Selection & projection
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Constructors
Readers
Writers
Filters
Find
Count
Functional thinking
mapcar 28/03/2017
• Goals – introduce
PS - Lisp Case study
• Database
4
• (setf sarah ‘((height 1.65) (weight 65)))  ((height 1.65) (weight 65))
• Retrieval is performed by
• (assoc <key> <association list>)
• (assoc ‘weight sarah)
• (second (assoc ‘weight sarah))
 (weight 65)
 65
• Advantages of a reader
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The data structure can be changed
Only the (internal) code for the reader need be changed
The functionality remains the same book‐author: book  author
You all knew that! 
PS - Lisp Case study
• Association list
• Contains sub‐lists: symbol (key) + value
28/03/2017
Lisp:CaseStudyDesignAspects
5
• Find the title
• Find the author
• Find the class
; Title
; Author
; Class
(second (assoc ‘title book‐ex2))
(second (assoc ‘author book‐ex2))
(second (assoc ‘class book‐ex2))
• Which can be generalised
PS - Lisp Case study
(setf book‐ex2
‘( (title
(Artificial Intelligence )) (author (Patrick Henry Winston)) (class
(Technical AI )) )
)
28/03/2017
Lisp:CaseStudy
(defun find (key object) (second (assoc key object)))
; definition
(find ‘title book‐ex2) ; call
(Artificial Intelligence)
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(attribute)
(setf book‐ex2
‘( (title
(Artificial Intelligence )) (author (Patrick Henry Winston )) (class (Technical AI )) )
; Title
; Author
; Class )
(defun book‐author (book) (second (assoc ‘author book))
(defun book‐title (book) (second (assoc ‘title book))
(defun book‐class (book) (second (assoc ‘class book))
function name‐‐‐‐‐parameter‐‐‐‐‐‐‐function body‐‐‐‐‐‐‐‐‐‐‐‐
Application (function call): (book‐author book‐ex2)
Value (application result): (Patrick Henry Winston)
PS - Lisp Case study
• readers – define a reader for each key 28/03/2017
Lisp:CaseStudy– reader
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(make‐book ‘(Common Lisp) ‘(Guy Steele) ‘(Technical Lisp)))
result:‐
((title (Common Lisp)) (author (Guy Steele)) (class (Technical Lisp)))
PS - Lisp Case study
• Constructor (note: literal symbols & parameter VALUES)
(defun make‐book (title author class)
(list
(list
‘title
title )
(list
‘author
author )
(list
‘class
class )))
>(setf book‐ex4 ; NB this is a writer (setter)
28/03/2017
Lisp:CaseStudy‐ constructor
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• (setf book‐ex make‐book(‐‐‐))
; writer
• (list (make‐book (‐‐‐) (make‐book (‐‐‐) …)
; create DB
• This list can in turn be
• Transformed
• Filtered
• All fiction books
• All authors
PS - Lisp Case study
• the constructor may be used in a writer • or to create a DB of books
28/03/2017
Lisp:CaseStudy‐ constructor
– list of author names
– according to some predicate
; selection (row)
; projection (col)
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Lisp:CaseStudy‐ writer
• Writers
>(defun book‐author‐writer (book author)
(if (eql 'author (first (first book)))
(cons (list 'author author) (rest book))
(cons (first book) (book‐author‐writer (rest book) author)))
)
>(setf book‐ex4 (book‐author‐writer book‐ex4 '(Guy L Steele)))
PS - Lisp Case study
((TITLE (COMMON LISP)) (AUTHOR (GUY STEELE)) (CLASS (TECHNICAL LISP))) 28/03/2017
>(setf book‐ex4 (make‐book '(Common Lisp) '(Guy Steele) '(Technical Lisp)) )
((TITLE (COMMON LISP)) (AUTHOR (GUY L STEELE)) (CLASS (TECHNICAL LISP))) 10
Lisp:CaseStudy:BookCollection
Patrick Henry
Winston
Common Lisp
Guy L Steele
Moby Dick
Herman Melville
Technical
AI
Technical
Lisp
Fiction
Tom Sawyer
Mark Twain
Fiction
The Black
Orchid
Rex Stout
Fiction
Mystery
PS - Lisp Case study
Artificial
Intelligence
28/03/2017
• The Library
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((PATRICK HENRY WINSTON) (GUY L STEELE) (HERMAN MELVILLE) (MARK TWAIN) (REX STOUT))
PS - Lisp Case study
>(defun list‐authors (books)
; empty list
(if (endp books)
nil
(cons (book‐author (first books))
; head / tail
(list‐authors (rest books)) ) ; (cons A B)
)
)
>(list‐authors books)
28/03/2017
Lisp:CaseStudy‐ projection
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Lisp:CaseStudy‐ selection
>(defun fictionp (book) (member 'fiction (book‐class book)) )
>(fictionp (third books))
(fiction)
Now use a programming cliché…
PS - Lisp Case study
>(defun book‐class (book) (second (assoc 'class book)))
>(book‐class (third books))
(fiction)
28/03/2017
Find all the books in class “fiction”
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; otherwise
; no – omit
1
2
3
PS - Lisp Case study
>(defun list‐fiction‐books (books)
(cond
((endp books) nil) ; empty list? ((fictionp (first books)) ; is fiction? (cons (first books)
; yes ‐ include
(list‐fiction‐books (rest books))))
(t (list‐fiction‐books (rest books)))
28/03/2017
Lisp:CaseStudy‐ selection
))
; (1) empty list (2) first book is fiction (3) default (t = true)
cond is if (A) exprA … elsif (B) exprB… else expr_default (logical switch!)
(cond (predicate1 expr1) (predicate2 expr2) … (t expr_default))
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Lisp:CaseStudy‐ selection
PS - Lisp Case study
(((TITLE (MOBY DICK)) (AUTHOR (HERMAN MELVILLE))
(CLASS (FICTION)))
((TITLE (TOM SAWYER)) (AUTHOR (MARK TWAIN))
(CLASS (FICTION)))
((TITLE (THE BLACK ORCHID)) (AUTHOR (REX STOUT))
(CLASS (FICTION MYSTERY))))
28/03/2017
>(list‐fiction‐books books)
>(length (list‐fiction‐books books)) ;how many?
3
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• mapcar – apply a function to each list element
(mapcar #’oddp ‘(1 2 3))  (T NIL T)
• List‐authors now becomes
>(mapcar #’book‐author books)
PS - Lisp Case study
• Lisp provides primitives to perform these actions (remove (filter), count & find (first))
28/03/2017
Lisp:CaseStudy– applyall
((PATRICK HENRY WINSTON) (GUY L STEELE) (HERMAN MELVILLE) (MARK TWAIN) (REX STOUT))
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Lisp:CaseStudy‐ count
#’fictionp books)
>(count‐if‐not #’fictionp books)
2
PS - Lisp Case study
>(count‐if
3
28/03/2017
• Counters: count‐if / count‐if‐not
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((TITLE (MOBY DICK)) (AUTHOR (HERMAN MELVILLE)) (CLASS (FICTION))) >(find‐if‐not #’fictionp books)
((TITLE (ARTIFICIAL INTELLIGENCE)) (AUTHOR (PATRICK HENRY WINSTON)) (CLASS (TECHNICAL AI)))
>(remove‐if #’fictionp books)
(((TITLE (ARTIFICIAL INTELLIGENCE)) (AUTHOR (PATRICK HENRY WINSTON))
(CLASS (TECHNICAL AI)))
((TITLE (COMMON LISP)) (AUTHOR (GUY L STEELE)) (CLASS (TECHNICAL LISP))))
PS - Lisp Case study
• Finders: find‐if / find‐if‐not ‐ finds the first occurrence
• Filters: remove‐if / remove‐if‐not
>(find‐if
#’fictionp books)
28/03/2017
Lisp:CaseStudy– find/remove
>(remove‐if‐not #’fictionp books)
(((TITLE (MOBY DICK)) (AUTHOR (HERMAN MELVILLE)) (CLASS (FICTION)))
((TITLE (TOM SAWYER)) (AUTHOR (MARK TWAIN)) (CLASS (FICTION)))
((TITLE (THE BLACK ORCHID)) (AUTHOR (REX STOUT)) (CLASS (FICTION MYSTERY))))
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(defun book‐title (book) (defun book‐author (book)
(defun book‐class (book) (defun fictionp
(book) (second (assoc 'title book)) ) (second (assoc 'author book)) )
(second (assoc 'class book)) ) (member 'fiction (book‐class book)) ) (mapcar #’<function> books) (remove‐if #’<predicate> books)
(find‐if
#’<predicate> books)
(count‐if #’<predicate> books)
; apply <function> to each element
; filter
; find first
; count
PS - Lisp Case study
(defun make‐book (title author class)
(defun baw (book author)
(list (list 'title title) (if (eql 'author (first (first book)))
(list 'author author) (cons (list 'author author) (rest book))
(list 'class class) )) (cons (first book) (baw (rest book) author)))))
28/03/2017
Lisp:CaseStudy:finalversion
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Lisp:CaseStudy
• first, rest
•
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•
•
association list (assoc)
setf
mapcar
remove‐if remove‐if‐not
find‐if
find‐if‐not
count‐if count‐if‐not
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•
•
•
•
•
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Constructor
Reader
Writer Filter
Find
Count
Apply function to each list element (mapcar)
28/03/2017
• primitive functions
• Clichés – (patterns)
PS - Lisp Case study
• Lisp constructs
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