;;;; The assignment is to fill in the definitions below, adding your code where ever ;;;; you see the comment ;; replace this line ;;;; to make each function do what its comments say it should do. You ;;;; may replace such a line with as many lines as you want to. You may ;;;; also add your own functions, as long as each function has a ;;;; comment like the ones below. You may not make any other changes ;;;; to this code. ;;;; see end of file for some examples that will run ONCE THE FUNCTION add-check ;;;; IS FILLED IN ;;;; See the assignment on Sakai for more examples (these may require ;;;; more than add-check to be filled in) and further information, ;;;; including due date. ;;;; code for a program to create closures that generate figures out ;;;; of characters. ;;; figures: a figure is represented by a list of 3 elements: func, ;;; numrows, and numcols where: ;;; func is a function (ie a closure) of two parameters: row, column ;;; that returns the character at the given row and column of the ;;; figure. If row is out of bounds ie row<0 or row>=numrows, or ;;; similarly for col, func returns the character #\. (a period ;;; character) ;;; numrows is the number of rows in the figure ;;; numcols is the number of columns in the figure ;;; The following are functions to create and access a figure. Note that ;;; make-figure adds bounds checking to func (define (make-figure func numrows numcols) (list (add-check func numrows numcols) numrows numcols)) (define (figure-func figure) (car figure)) (define (figure-numrows figure)(cadr figure)) (define (figure-numcols figure)(caddr figure)) ;;; forn takes three arguments: start and stop, which are numbers, and func ;;; which is a function of one argument. ;;; forn calls func several times, first with the argument start, then with start+1 ;;; then ... finally with stop. It returns a list of the values of the calls. ;;; If start>stop, forn simply returns the empty list without doing any calls to func. (define (forn start stop func) (if (> start stop) '() (let ((first-value (func start))) (cons first-value (forn (+ 1 start) stop func))))) ;;; range-check takes 4 arguments: row, numrows, col, numcols It checks if ;;; 0 <= row < numrows and similarly for col and numcols. If both row and col are in ;;; range, range-check returns #t. If either are out of range, rangecheck returns #f (define (range-check row numrows col numcols) (not (or (< row 0) (< col 0) (>= row numrows) (>= col numcols)))) ;;; add-check takes 3 arguments: func, numrows and numcols. func is a ;;; function of two numbers, row and col. add-check returns a new ;;; function, which we will refer to here as func2. Like func, func2 takes ;;; a row number and a column number as arguments. func2 first calls ;;; range-check to do a range check on these numbers against numrows ;;; and numcols. If row or col is out of range func2 returns #\., ;;; otherwise it returns the result of (func row col). You can think of ;;; func2 as a "safe" version of func, like the function returned by ;;; null-safe in Resources > Scheme > null-safe.scm except that a ;;; "bad", i.e. out of range, argument to func here will not necessarily ;;; crash scheme the way (car '( )) would. (define (add-check func numrows numcols) ' ( ) ;; replace this line ) ;;; display-window prints out the characters that make up a rectangular segment of the figure ;;; startrow and endrow are the first and last rows to print, similarly for startcol and endcol ;;; The last thing display-window does is to call (newline) to print a blank line under the figure. (define (display-window start-row stop-row start-col stop-col figure) (forn start-row stop-row (lambda (r) (forn start-col stop-col (lambda (c) (display ((figure-func figure) r c)))) (newline))) (newline)) ;;; charfig take one argument, a character, and returns a 1-row, 1-column figure consisting of that character (define (charfig char) (make-figure (lambda (row col) char) 1 1)) ;;; sw-corner returns a figure that is a size x size square, in which ;;; the top-left to bottom-right diagonal and everything under it is ;;; the chracter * and everything above the diagonal is the space ;;; character (define (sw-corner size) (make-figure (lambda (row col) (if (>= row col) #\* #\space)) size size)) ;;; repeat-cols returns a figure made up of nrepeat copies of ;;; figure, appended horizontally (left and right of each other) (define (repeat-cols nrepeat figure) (make-figure (lambda (row col) ((figure-func figure) row (modulo col (figure-numcols figure)))) (figure-numrows figure) (* nrepeat (figure-numcols figure)) ;; the function just calls the function that repeat-cols received, but ;; uses modulo to select the right position. )) ;;; repeat-rows returns a figure made up of nrepeat copies ;;; of a figure, appended vertically (above and below each other) (define (repeat-rows nrepeat figure) ' ( ) ;; replace this line ) ;;; append cols returns the figure made by appending figureb to the ;;; right of figurea the number of rows in the resulting figure is the ;;; smaller of the number of rows in figurea and figureb (define (append-cols figurea figureb) '( ) ;; replace this line ) ;;; append-rows returns the figure made by appending figureb below figurea ;;; the number of columns in the resulting figure is the smaller of the number of columns in figurea ;;; and figternb (define (append-rows figurea figureb) '( );; replace this line ) ;;; flip-cols returns a figure that is the left-right mirror image of figure (define (flip-cols figure) '( ) ;;replace this line ) ;;; flip-rows returns a figure that is the up-down mirror image of figure (define (flip-rows figure) '( ) ;; replace this line ) ;;;; some examples thst should work after just add-check is filled in ;;;; above. (Remove the ;'s at the start of the lines below.) ;(define fig1 (sw-corner 4)) ;(display-window 0 3 0 3 fig1) ;(define fig2 (repeat-cols 3 fig1)) ;(display-window 0 4 ; 0 12 fig2)