1 / 36

Functional Programming

Functional Programming. 06 Input and Output. Streams. Two kinds of streams Character streams Binary streams Character streams are Lisp objects representing sources and/or destinations of characters

daxia
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 06 Input and Output

  2. Streams • Two kinds of streams • Character streams • Binary streams • Character streams are Lisp objects representing sources and/or destinations of characters • To read from or write to a file, you open it as a stream, but streams are not identical with files • When you read or print at the toplevel, you also use a stream

  3. Streams Default input is read from the stream *standard-input* Default output is write to *standard-output* Initially *standard-input* and *standard-output* will be the same place: a stream presenting the toplevel

  4. Streams • Make the file • > (setf path (make-pathname:name “myfile”))#P”myfile” • Open the file • > (setfstr (open path :direction :output :if-exists :supersede))#<BUFFERED FILE-STREAM CHARACTER #P”myifle” @1> • Write to the stream • > (format str “Something~%”)NIL • Close the stream • > (close str)NIL

  5. Streams • Read the file • Open a stream with :direction :input • > (setfstr (open path :direction :input)) #<BUFFERED FILE-STREAM CHARACTER #P”myifle” @1> • > (read-line str)“Something” • with-open-file macro • > (with-open-file (str path :direction :output :if-exists :supersede) (format str “Something~%”)) • The stream is automatically closed

  6. Input • Most popular input functions • read-line • read • > (progn (format t “Please enter your name: “) (read-line))Please enter your name: Rodrigo de Bivar“Rodrigo de Bivar”NIL → is true only if read-line ran out of input before encountering a newline

  7. Input • (defun pseudo-cat (file) (with-open-file (str file :direction :input) (do ((line (read-line str nil ‘eof) (read-line str nil ‘eof))) ((eql line ‘eof)) (format t “~A~%” line)))) • If you want input parsed into Lisp objects, use read • > (read)(abc)(A B C)

  8. Output • Three simplest output functions • prin1 • Generates output for programs • > (prin1 “Hello”)“Hello”“Hello” • princ • Generates output for people • > (princ “Hello”)Hello“Hello” • terpri • Prints a new line

  9. Output • format • > (format nil “Dear ~A, ~% Our records indicate…” “Mr. Malatesta”)“Dear Mr. Malatesta, Our records indicate…” • > (format t “~S~A” “z” “z”)“z” zNIL

  10. Output • > (format nil “~10,2,0,’*, ‘ F” 26.21875)“ 26.22” • Rounded to 2 decimal places • With the decimal point shifted right 0 places • Right-justified in a field of 10 characters • Padded on the left by blanks • If it is too long to fit in the space allowed by the first argument, the character * is printed • > (format nil “~,2,,,F” 26.21875)“26.22” • > (format nil “~,2F” 26.21875)“26.22”

  11. Review – Function pointer in C 1#include <iostream>23using namespace std; 45void printArrayOdd(int* beg, int* end) {6  while(beg != end) { 7    if ((*beg)%2) 8 cout << *beg << endl; 910    beg++;11  }12}1314void printArrayEven(int* beg, int* end) {15  while(beg != end) {16    if (!((*beg)%2))17 cout << *beg << endl;1819    beg++;20  }21}22

  12. Review – Function pointer in C 23void printArrayGreaterThan2(int* beg, int* end) {24  while(beg != end) {25    if ((*beg)>2)26 cout << *beg << endl;27      28    beg++;29  }30}3132int main() {33intia[] = {1, 2, 3};3435cout << "Odd" << endl;36printArrayOdd(ia, ia + 3);3738 39cout << "Even" << endl;40printArrayEven(ia, ia + 3);4142cout << "Greater than 2" << endl;43  printArrayGreaterThan2(ia, ia + 3);44} Execution results Odd13Even2Greater than 23

  13. Review – Function pointer in C 1/**//* 2  (C) OOMusou 2007 http://oomusou.cnblogs.com34Filename    : FuntionPointer.cpp5Compiler    : Visual C++ 8.0 / BCB 6.0 / gcc 3.4.2 / ISO C++6Description : Demo how to use function pointer7Release     : 05/01/2007 1.08*/9#include <iostream>1011using namespace std;1213typedef bool (*predicate)(int);1415bool isOdd(inti) {16  return i%2? true : false;17}1819boolisEven(inti) {20  return i%2? false : true;21}22

  14. Review – Function pointer in C 23bool greaterThan2(inti) {24  return i > 2;25}2627void printArray(int* beg, int* end, predicate  fn) {28  while(beg != end) {29    if ((*fn)(*beg))30cout << *beg << endl;3132    beg++;33  }34}3536int main() {37intia[] = {1, 2, 3};3839cout << "Odd" << endl;40printArray(ia, ia + 3, isOdd);4142cout << "Even" << endl;43printArray(ia, ia + 3, isEven);4445cout << "Greater than 2" << endl;46printArray(ia, ia + 3, greaterThan2);47} Execution results Odd13Even2Greater than 23

  15. Review – Function pointer in C • By using function pointer, C can pass a function as an argument to another function • C++ and C# also provide similar idea • C++: Function object (Functor) • C# (pronounced as C sharp): Delegate • But…., how to return a function? • C also could return a function pointer • http://www.newty.de/fpt/fpt.html • However, it needs more complex consideration to write such a function with higher feasibility

  16. Review – Closure • Functional programming languages use “closures” to provide feasibility of functions, so that returning a function becomes easier and more practical • (defun make-adder (n) #’(lambda (x) (+ x n))) → returns a function • (setf add3 (make-adder 3))#<CLOSURE: LAMBDA (X) (+ X N)> • > (funcall add3 2)5

  17. Review > (list ‘my (+ 2 1) “Sons”)(MY 3 “Sons”) > (list ‘(+ 2 1) (+ 2 1))((+ 2 1) 3) > (cons ‘a ‘(b c d))(A B C D) > (cons ‘a (cons ‘b nil))(A B) > (car ‘(a b c))A > (cdr ‘(a b c))(B C)

  18. Review > (setf x (list ‘a ‘b ‘c))(A B C) > (setf (car x ) ‘n)N> x(N B C)

  19. Review • > (apply #’+ ‘(1 2 3))6 • > (mapcar#’(lambda (x) (+ x 10)) ‘(1 2 3))(11 12 13) • > (mapcar#’list ‘(a b c) ‘(1 2 3 4))((A 1) (B 2) (C 3)) • > (maplist#’(lambda (x) x) ‘(a b c))((A B C) (B C) (C))

  20. Review • > (member ‘b ‘(a b c))(B C) • > (member ‘(b) ‘((a) (b) (c)))NIL Why? • Equal: the same expression? • Eql: the same symbol or number? • member compares objects using eql • > (member ‘(a) ‘((a) (z)) :test #’equal) ;:test-> keyword argument((A) (Z)) • > (member ‘a ‘((a b) (c d)) :key #’car)((A B) (C D)) • Ask if there is an element whose car is a

  21. Review > (subseq ‘(a b c d) 1 2)(B) > (every #’oddp ‘(1 3 5)) ;everyone is …T > (some #’evenp ‘(1 2 3)) ;someone is …T > (every #’> ‘(1 3 5) ‘(0 2 4))T

  22. Review • Dotted list:is an n-part data structure • (A . B) • (setf pair (cons ‘a ‘b))(A . B) • > ‘(a . (b . (c . nil)))(A B C) • > (cons ‘a (cons ‘b (cons ‘c ‘d)))(A B C . D)

  23. Review • make-array • > (setfarr (make-array ‘(2 3) :initial-element nil))#<Array T (2 3)> • Maximum: • 7 dimensions • Each dimension can have 1023 elements • Initial-element • Optional • Whole array will be initialized to this value • > (arefarr 0 0)NIL • > (setf(arefarr 0 0) ‘b)B • > (arefarr 0 0) ; access the arrayB

  24. Review • One-dimensional array • > (setfvec (make-array 4 :initial-element nil))#(NIL NILNILNIL) • > (vector “a” ‘b 5 “c”)#(“a” B 5 “c”) • > (setfvec (vector “a” ‘b 5 “c”)) > (svrefvec 1) ;access the vector (sv: simple vector)B • String: a vector of characters • > (sort “elbow” #’char<)“below” • Retrieve an element of a string • > (aref “abc” 1)#\b • > (char “abc” 1)#\b

  25. Review • Replace elements of a stirng • > (let ((str (copy-seq “Merlin”))) (setf (char str 3) #\k)str)“Merkin” • Compare two strings • > (equal “fred” “fred”)T • > (equal “fred” “Fred”)NIL • > (string-equal “fred” “Fred”)T • Building strings • > (format nil “~A or ~A” “truth” “dare”)“truth or dare” • > (concatenate ‘string “not “ “to worry”)“not to worry”

  26. Review > (progn (format t “a”) (format t “b”)(+ 11 12))ab23 -> only the value of the last expression is returned > (block head (format t “Here we go.”) (return-from head ‘idea) (format t “We’ll never see this.”))Here we go.

  27. Review • > (let ((x 7) (y 2)) (format t “Number”) (+ x y))Number9 • >((lambda (x) (+ x 1)) 3)4 • (let ((x 2) (y (+ x 1))) (+ x y)) • ((lambda (x y) (+ x y)) 2 (+ x 1))

  28. Review (if <test> <then form> <else form>) (if <test> <then form>)(when <test> <then form>) (if <test> nil <else form>) (unless <test> <else form>)

  29. Review • cond • (cond (<test 1> <consequent 1-1> …) (<test 2> <consequent 2-1> …) … (<test m> <consequent m-1> …));cond • case • (case <key form> (<key 1> <consequent 1-1> …) (<key 2> <consequent 2-1> …) ... (<key m> <consequent m-1> …)) ;case

  30. Review • do • (do ((<parameter 1> <initial value 1> <update form 1>) (<parameter 2> <initial value 2> <update form 2>) … (<parameter n> <initial value n> <update form n>)) (<termination test> <intermediate forms, if any> <result form>) <body>) ;do • > (let ((x ‘a)) (do ((x 1 (+ x 1)) (y x x)) ((> x 5)) (format t “(~A ~A) “ x y)))(1 A) (2 1) (3 2) (4 3) (5 4) ;on each iteration, x gets its previousNIL ;value plus 1; y also gets the previous ;value

  31. Review • do* • Has the same relation to do as let* does to let • > (do* ((x 1 (+ x 1)) (y x x)) ((> x 5)) (format t “(~A ~A) “ x y))(1 1) (2 2) (3 3) (4 4) (5 5)NIL

  32. Review • dolist • > (dolist (x ‘(a b c d) ‘done) (format t “~A “ x))A B C DDONE • dotimes • > (dotimes (x 5 x) ; for x = 0 to 5-1, return x (format t “~A “ x))0 1 2 3 4 5

  33. Review • Multiple values • > (values ‘a nil (+ 2 4))ANIL6 • (labels ((add10 (x) (+ x 10)) (consa (x) (cons ‘a x))) (consa (add10 3)))(A . 13) • > (labels ((len (lst) (if (null lst) 0 (+ (len (cdrlst)) 1)))) (len ‘(a b c)))3

  34. Review • (defun our-funcall (fn &restargs) (apply fn args)) • > (defunkeylist (a &key x y z) (list a x y z))

  35. Review (defun disjoin (fn &rest fns) (if (null fns) fn (let ((disj (apply #’disjoin fns))) #’(lambda (&rest args) (or (apply fn args) (apply disjargs)))))) > (mapcar (disjoin #’integerp #’symbolp) ‘(a “a” 2 3))(T NIL T T)

  36. Midterm exam • Time: April 21 • Classroom: 資工所(應用科學大樓)/B1演講廳

More Related