1. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 1 66-2210-01 Programming in Lisp Data Abstraction and Mapping

2. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 2 Data Representation  Record course information –Basic definition (setf course-1 '(66221001; course number (Programming in Lisp); course name (Alok Mehta); instructor (Computer Science))); department –What is the name of ‘course-1’? > (second course-1) (Programming in Lisp) –Poor practice - Depends on the ordering of the list –What if order changes, or, you need to add something to the list (setf course-1 '(66221001 1; Credit hours (Programming in Lisp); Course name (Alok Mehta); Instructor (Computer Science))); Department –All programs that access name of course-1 have to change > (third course-1)

3. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 3 Association Lists  How do you know ‘1’ represents credit hours?  Better way to represent data: Association Lists (setf course-1 '( (course-number 66221001) (credit-hours 1) (name (Programming in Lisp)) (instructor (Alok Mehta)) (department (Computer Science))))  What is the name of ‘course-1’? > (second (third course-1)) (PROGRAMMING IN LISP) > (assoc 'name course-1) (NAME (PROGRAMMING IN LISP)) > (second (assoc 'name course-1) (PROGRAMMING IN LISP)

4. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 4 Simple Database  A database as a list of “records” (setf course-database '( ((course-number 66221001) (credit-hours 1) (name (Programming in Lisp)) (instructor (Alok Mehta)) (department (Computer Science))) ((course-number 66220001) (credit-hours 1) (name (Programming in C++)) (instructor (Louis Ziantz))) ))  What is the name? (second (assoc 'name (first course-database)))

5. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 5 Access Functions  Write functions to access low-level details (defun get-course-name (course) (second (assoc 'name course))) –Don’t have to remember how data is stored –Can change storage details easily –Access to data is achieved at a higher level –Easier to read and understand –More maintainable code  Write functions to construct and manipulate data (defun make-course (&key course-number credit-hours name instructor department) (list (list 'course-number course-number) (list 'credit-hours credit-hours) (list 'name name) (list 'instructor instructor) (list 'department department) ))

6. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 6 Calling Access Functions > (setf course-1 (make-course :name '(Programming in Java) :instructor ’(Alok Mehta))) ((COURSE-NUMBER NIL) (CREDIT-HOURS NIL) (NAME (PROGRAMMING IN JAVA)) (INSTRUCTOR (ALOK MEHTA)) (DEPARTMENT NIL)) > (get-course-name course-1) (PROGRAMMING IN JAVA)

7. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 7 A simple database example (setf courses (list (make-course :course-number '66220001 :name '(Programming in C++) :instructor '(Louis Ziantz)) (make-course :course-number '66221001 :name '(Programming in Lisp) :instructor '(Alok Mehta)) (make-course :course-number '66222001 :name '(Programming in Java) :instructor '(Alok Mehta)) (make-course :course-number '66223001 :name '(Programming in Perl) :instructor '(Louis Ziantz)) ))

8. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 8 Which courses are offered?  Example Usage > (get-course-numbers courses) (66220001 66221001 66222001 66223001) (defun get-course-number (course) (second (assoc 'course-number course))) (defun get-course-numbers (course-list) (if (endp course-list) NIL (cons (get-course-number (first course-list)) (get-course-numbers (rest course-list)))))  Implements a “Transformation” SQL Equivalent: SELECT course_number FROM courses;

9. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 9 Which are taught by Alok?  List the courses taught by Alok Mehta > (get-courses-taught-by-alok courses) (((COURSE-NUMBER 66221001) …) ((COURSE-NUMBER 66222001)...)...) (defun get-course-instructor (course) (second (assoc 'instructor course))) (defun taught-by-alok-p (course) (if (equal '(Alok Mehta) (get-course-instructor course)) t NIL)) (defun get-courses-taught-by-alok (course-list) (cond ((endp course-list) NIL) ((taught-by-alok-p (first course-list)) (cons (first course-list) (get-courses-taught-by-alok (rest course-list)))) (t (get-courses-taught-by-alok (rest course-list)))))

10. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 10 How many are taught by Alok  List the courses taught by Alok Mehta [Filter] > (get-courses-taught-by-alok courses)  Implements “Filtering” SQL: SELECT * FROM COURSES WHERE instructor = ‘Alok Mehta’;  How many courses are taught by Alok? [Count] > (length (get-courses-taught-by-alok courses)) 2 SQL: SELECT COUNT(*) FROM COURSES WHERE instructor = ‘Alok Mehta’;  What is the first course taught by Alok? [Find] > (first (get-courses-taught-by-alok courses)) ((COURSE-NUMBER 66221001) (CREDIT-HOURS NIL) (NAME (PROGRAMMING IN LISP)) (INSTRUCTOR (ALOK MEHTA)) (DEPARTMENT NIL))

11. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 11 More efficient way to Count  A more efficient way to count  Don’t have to get all courses first! (defun count-courses-taught-by-alok (course-list) (cond ((endp course-list) 0) ((taught-by-alok-p (first course-list)) (+ 1 (count-courses-taught-by-alok (rest course-list)))) (t (count-courses-taught-by-alok (rest course-list)))))  A more efficient way to find first course (defun find-first-course-taught-by-alok (course-list) (cond ((endp course-list) nil) ((taught-by-alok-p (first course-list)) (first course-list)) (t (find-first-course-taught-by-alok (rest course-list)))))

12. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 12 Cliches  Many procedures have a common template (defun (input-list) (if (endp input-list) nil (cons ( (first input-list)) ( (rest input-list)))))  Example: –List-transformer: get-course-numbers –Element-transformer: get-course-number (defun get-course-numbers (course-list) (if (endp course-list) NIL (cons (get-course-number (first course-list)) (get-course-numbers (rest course-list)))))  This template is frequently used  Lisp has a primitive (MAPCAR) to make this easier

13. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 13 Mapcar  MAPCAR (mapcar ) Applies to each element of  Example > (mapcar #'oddp '(1 2 3)) (T NIL T) > (mapcar #'get-course-number courses) (66220001 66221001 66222001 66223001) > (mapcar #'= '(1 2 3) '(3 2 1)) (NIL T NIL)

14. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 14 Remove-If, Remove-If-Not  Remove-If, Remove-If-Not > (remove-if-not #'taught-by-alok-p courses) [Removes all courses for which “taught-by-alok-p” returns NIL] This will return all courses taught by Alok > (remove-if #'taught-by-alok-p courses) [Removes all courses for which “taught-by-alok-p” returns non-NIL] This will return all courses NOT taught by Alok  Count-If, Count-If-Not > (count-if #'taught-by-alok-p courses) Counts the number of elements for which “taught-by-alok-p” returns non-NIL  Find-If, Find-If-Not > (find-if #'taught-by-alok-p courses) Returns the FIRST element of courses for which “taught-by-alok-p” returns non- NIL

15. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 15 Funcall  Funcall –Template (funcall #' … ) Calls the specified procedure with the given argments –Equivalent to ( … ) –Example > (funcall #'+ 3 2 7) ;; Same as (+ 3 2 7) 12 –Example 2 > (defun eval-infix (arg1 operator arg2) (funcall operator arg1 arg2)) > (eval-infix 3 #'+ 2)  Useful if you need to pass in a procedure name, to be applied at a future time

16. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 16 Apply  Apply  Similar to Funcall  (typically) takes two arguments, –procedure object –list of arguments to be passed to procedure object (funcall #'+ 3 2 7) ;; Same as (+ 3 2 7) (apply #'+ '(3 2 7)) ;; Same as (+ 3 2 7)  Apply can actually take additional arguments –Extra arguments are combined into a single list –Following are equivalent (apply #'+ '(1 2 3 4 5 6)) (apply #'+ 1 2 3 '(4 5 6)) Argument fed to + is (append (list 1 2 3) ‘(4 5 6))

17. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 17 Lambda Procedures  Useful if you need an “anonymous” procedure  Don’t want to give it a name –A named procedure (defun taught-by-alok-p (course) (if (equal '(Alok Mehta) (get-course-instructor course)) t NIL)) –An equivalent un-named procedure (lambda (course) (if (equal '(Alok Mehta) (get-course-instructor course)) t NIL)) –Example usage: How many courses are taught by Alok? (count-if #'(lambda (course) (if (equal '(Alok Mehta) (get-course-instructor course)) t NIL)) courses)

18. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 18 Lambda procedures  Advantage  Don’t have to make up names for procedures  Definition of procedure is close to where it is used (defun get-courses-taught-by-alok (course-list) (remove-if-not #'(lambda (x) (equal '(Alok Mehta) (get-course-instructor x))) course-list))

19. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 19 Summary  Use readers, constructors, and writers  To hide data details  Transform, Filter, Count, Find are common  Can be defined recursively  Built-in functions in Lisp make things easier  Mapcar, Remove-If(Not), Count-If(Not), Find-If(Not)  Funcall, Apply  Lambda

20. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 20 Iteration  DOTIMES (Review) (dotimes ( ) ) –Example (dotimes (i 5) (print i)) ;; prints 0 1 2 3 4  DOLIST (dolist ( ) ) –Example (dolist (elem '(a b c d)) (print elem)) ;; prints a b c d

21. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 21 Example of DOLIST  Given a list of ages of people, how many adults? –List of ages > (setf ages '(3 4 17 21 22 34 2 7)) –Adult defined as: >= 21 years old > (defun adultp (age) (>= age 21)) –Using Count-if (defun count-adult (ages) (count-if #'adultp ages)) –Using dolist (defun count-adult (ages &aux (nadult 0)) (dolist (age ages nadult) (if (adultp age) (setf nadult (+ 1 nadult)))))

22. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 22 Example (cont.)  Get the ages of the first two adults (defun first-two-adults (ages &aux (nadult 0) (adults nil)) (dolist (age ages) (if (adultp age) (progn (setf nadult (+ nadult 1)) (push age adults) (if (= nadult 2) (return adults))))))  Notes  PROGN (and PROG1) are like C/C++ Blocks { … } > (prog1 (setf a 'x) (setf b 'y) (setf c 'z)) X > (progn (setf a 'x) (setf b 'y) (setf c 'z)) Z  RETURN exits the DOLIST block –Note: does not necessarily return from the procedure! –Takes an optional return value

23. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 23 DO  DO is more general than DOLIST or DOTIMES  Example (defun do-expt (m n) ;; Return M^N (do ((result 1) ;; Bind variable ‘Result’ to 1 (exponent n)) ;; Bind variable ‘Exponent’ to N ((zerop exponent) result) ;; test and return value (setf result (* m result)) ;; Body (setf exponent (- exponent 1)) ;; Body  Equivalent C/C++ definition int do_expt (int m, int n) { int result, exponent; for (result=1,exponent=n; (exponent != 0); ) { result = m * result; exponent = exponent - 1; } return result; }

24. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 24 DO Template  Full DO Template (There is also a DO*) (DO ( ( ) ( ) … ( ) ) ( … )  Rough equivalent in C/C++ for ( =, =,…, = ; //Note: Lisp=parallel !( ); // C/C++ has a “continuation-test” =, =,…, = ) { } ; ; … ; ; ; // Note: (DO…) in Lisp evaluates to // Note:,,…, are now restored to original values

25. Alok Mehta - Programming in Lisp - Data Abstraction and Mapping 25 Do-expt, Loop  Here is another (equivalent) definition of do-expt (defun do-expt (m n) (do ((result 1 (* m result)) (exponent n (- exponent 1))) ((zerop exponent) result) ;; Note that there is no body! ))  Loop  An infinite loop, terminated only by a (return) (loop (print '(Say uncle)) (if (equal (read) 'uncle) (return)))