1 / 26

Functional Programming

Functional Programming. 07 Symbols and Numbers. Symbols - Symbol Names. A symbol can have any string as its name > (symbol-name ‘ abc ) “ABC” The name of the symbol is all uppercase letters Common Lisp is not case-sensitive > ( eql ‘ aBc ‘ Abc ) T > ( CaR ‘(a b c) A.

yitta
Download Presentation

Functional Programming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Functional Programming 07 Symbols and Numbers

  2. Symbols - Symbol Names • A symbol can have any string as its name • > (symbol-name ‘abc)“ABC” • The name of the symbol is all uppercase letters • Common Lisp is not case-sensitive • > (eql ‘aBc ‘Abc)T • > (CaR ‘(a b c)A

  3. Symbols - Symbol Names • Use vertical bars to denote a symbol • > (list ‘|Lisp 1.5| ‘|| ‘|abc| ‘|ABC|)(|Lisp 1.5| || |abc| |ABC|) • When the name of such a symbol is read, there is no case conversion • > (symbol-name ‘|a b c|)“a b c”

  4. Symbols - Property Lists • Every symbol has a property list (plist) • > (get ‘alizarin ‘color)NIL • > (setf (get ‘alizarin ‘color) ‘red)RED • > (get ‘alizarin ‘color)RED • > (setf (get ‘alizarin ‘transparency) ‘high)HIGH • > (symbol-plist ‘alizarin)(TRANSPARENCY HIGH COLOR RED)

  5. Symbols - Symbols Are Big • Symbol is a substantial object

  6. Symbols - Symbols Are Big • Symbols are real objects, not just names • When two variables are set to the same symbol, it’s the same as when two variables are set to the same list • Both variables have pointers to the same object

  7. Symbols - Creating Symbols • Packages are symbol-tables, mapping names to symbols • Every ordinary symbol belongs to a particular package • A symbol that belongs to a package is said to be interned in that package • The first time you type the name of a new symbol • Lisp will create a new symbol object • Lisp will intern it in the current package

  8. Symbols - Multiple Packages • Larger programs are often divided up into multiple packages • If each part of a program is in its own package, then someone working on one part of the program will be able to use a symbol as the name of a function or variable without worrying that the name is already used elsewhere

  9. Symbols - Multiple Packages • (defpackage :package-test (:use “COMMON-LISP” “MY-UTILITIES”) (:nicknames :test) (:export :a :b))(in-package :test) • Define a new package called my-application • Uses two other packages: COMMON-LISP and MY-UTILITIES • Nickname is app • The my-application package itself exports three symbols: win, lose, and draw • Code in other packages will be able to refer to them as e.g. test:a

  10. Symbols - Multiple Packages • > (make-package :bob) #<Package BOB> • > (make-package :jane) #<Package JANE> • > (in-package :bob) #<Package BOB> • > (setf a 33) 33 • > a33 • > (in-package :jane) #<Package JANE> • > (setf a 55) 55 • > a55

  11. Symbols - Multiple Packages • If Jane wants to use a function written by Bob • > (in-package :jane) #<Package JANE> • > bob::a33

  12. Symbols - Keywords • Symbols in the keyword package (keywords) • They always evaluate to themselves • You can refer to them anywhere simply as :x, instead of keyword:x, e.g. (member ‘(a) ‘((a) (z)) :test #’equal) • (defun noise (animal) (case animal (:dog :woof) (:cat :meow) (:pig :oink)))

  13. Symbols - Example: Random Text • If you are going to write programs that operate on words, it’s often a good idea to use symbols instead of strings • Symbols can be compared in one step with eql • Strings have to be compared charater-by-character with string-equal or string= • > (read-text “..\\test\\test.txt”) • > (hash-table-count *words*) • > (generate-text 100)

  14. Symbols - Example: Random Text (defparameter *words* (make-hash-table :size 10000)) (defconstantmaxword 100) (defun read-text (pathname) (with-open-file (s pathname :direction :input) (let ((buffer (make-string maxword)) (pos 0)) (do ((c (read-char s nil :eof) (read-char s nil :eof))) ((eql c :eof)) (if (or (alpha-char-p c) (char= c #\’)) (progn (setf (aref buffer pos) c) (incf pos)) (progn (unless (zerop pos) (see (intern (string-downcase (subseq buffer 0 pos)))) (setf pos 0)) (let ((p (punc c))) (if p (see p)))))))))

  15. Symbols - Example: Random Text (defunpunc (c) (case c (#\. ‘|.|) (#\, ‘|,|) (#\; ‘|;|) (#\! ‘|!|) (#\? ‘|?|) )) (let ((prev ‘|.|)) (defun see (symb) (let ((pair (assoc symb (gethashprev *words*)))) (if (null pair) (push (cons symb 1) (gethashprev *words*)) (incf (cdr pair)))) (setfprevsymb)))

  16. Symbols - Example: Random Text (defun generate-text (n &optional (prev ‘|.|)) (if (zerop n) (terpri) (let ((next (random-next prev))) (format t “~A “ next) (generate-text (1- n) next)))) (defun random-next (prev) (let* ((choices (gethashprev *words*)) ( i (random (reduce #’+ choices :key #’cdr )))) (dolist (pair choices) (if (minusp(decf i (cdr pair))) (return (car pair))))))

  17. Term Project • Due: June 27 • Write a program to analyze the input article and produce: • The title of the article • The abstract of the article • Explain your evaluation strategies to decide whether a title or an abstract is suitable for this article • Requirements • Program demo • Detailed report

  18. Numbers - Types • Four types of numbers • Integer 2001 • Floating-point number 253.72 or 2.5372e2 • Ratio 2/3 • Complex number #c(a b) is a+bi • Predicates for numbers • integerp • floatp • complexp

  19. Numbers - Types • Rules for determining what kind of number a computation will return • If a numeric function receives one or more floating-point numbers as arguments, the return value will be a floating-point number (or a complex number with floating-point components) • (+ 1.0 2) evaluates to 3.0 • (+ #c(0 1.0) 2) evaluates to #c(2.0 1.0) • Ratios that divide evenly will be converted into integers • (/ 10 2) returns 5 • Complex numbers whose imaginary part would be zero will be converted into reals • (+ #c(1 -1) #c(2 1)) returns 3 • > (list (ratiop 2/2) (complexp #c(1 0)))??

  20. Numbers – Conversion and Extraction • > (mapcar #’float ‘(1 2/3 .5))(1.0 0.6666667 0.5) • > (truncate 1.3)10.29999995 • floor • ceiling • (defun our-truncate (n) (if (> n 0) (floor n) (ceiling n)))

  21. Numbers – Conversion and Extraction • round: retuns the nearest even digit • > (mapcar #’round ‘(-2.5 -1.5 1.5 2.5))(-2 -2 2 2) • signum: returns either 1, 0, or -1, depending on whether its argument is positive, zero, or negative • (* (abs x) (signum x)) = x

  22. Numbers – Comparison • > (= 1 1.0)T • > (eql 1 1.0)NIL • > (equal 1 1.0)?? • (<= w x y z) ≡ (and (<= w x) (<= x y) (<= y z)) • (/= w x y z) ≡ (and (/= w x) (/=w y) (/= w z) (/= x y) (/=x z) (/= y z)) • > (list (minusp -0.0) (zerop -0.0))(NIL T) • > (list (max 1 2 3 4 5) (min 1 2 3 4 5))(5 1)

  23. Numbers – Arithmetic • (- x y z) ≡ (- (- x y) z) • (-1 x) returns x-1 • (incf x n) ≡ (setf x (+ x n))(decf x n) ≡ (setf x (- x n)) • > (/ 365 12)365/12 • > (float 365/12)30.416666 • > (/ 3)1/3 • (/ x y z) ≡ (/ (/ x y) z)

  24. Numbers – Exponentiation • (expt x n) → • > (expt 2 5)32 • (log x n) → • (log 32 2)5.0 • > (exp 2)7.389056 • > (log 7.389056)2.0 • > (expt 27 1/3)3.0 • > (sqrt 4)2.0

  25. Homework • Modify the following program (defun mirror? (s) (let ((len (length s))) (and (evenplen) (let ((mid (/ len 2))) (equal (subseq s 0 mid) (reverse (subseq s mid))))))) to recognize all palindromes

  26. Homework • (defun palindrome? (x) (let ((mid (/ (length x) 2))) (equal (subseq x 0 (floor mid)) (reverse (subseq x (ceiling mid))))))

More Related