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Diffstat (limited to 'hw02.scm')
| -rw-r--r-- | hw02.scm | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/hw02.scm b/hw02.scm new file mode 100644 index 0000000..9f551a4 --- /dev/null +++ b/hw02.scm @@ -0,0 +1,156 @@ +#lang scheme + +;; PROGRAM NAME: hw02.rkt +;; DESCRIPTION: Homework 2 for CSI 310 +;; AUTHOR: Ben Burwell +;; HISTORY: Turned in 2013-01-29 +;; NOTES: When this program runs, a series of expected and +;; actual results will print out. Compare them to +;; ensure the code functions properly. + +;; ============ PROCEDURE ============ +;; NAME: invert +;; +;; DESC: +;; takes a list of 2-lists and inverts each of the lists +;; hence, the list +;; ((2 1) (4 3) (6 5)) +;; will become +;; ((1 2) (3 4) (5 6)) + +(define invert + (λ (lst) + (cond + [ (null? lst) null ] + [ (not (list? lst)) (display "Invalid Parameters") ] + [ (null? (cdr lst)) (list (invert-reverse (car lst))) ] + [ else (append (list (invert-reverse (car lst))) (invert (cdr lst))) ] ))) + +;; a helper function that reverses a 2-list +;; PRECONDITION: lst is a list of the form (a b) +;; POSTCONDITION: lst is a list of the form (b a) +;; ERROR: lst is not a list with 2 elements +(define invert-reverse + (λ (lst) + (cond + [ (null? lst) null ] + [ (not (list? lst)) (display "Invalid Parameters") ] + [ (not (equal? (length lst) 2)) (display "Invalid Parameters") ] + [ else (list (cadr lst) (car lst)) ] ))) + +;; ============ TEST CODE ============ +(newline) +(display "Testing (invert) =========================================") +(newline) + +(display "Expected output: () ") +(invert '()) + +(display "Expected output: ((1 2)) ") +(invert '((2 1))) + +(display "Expected output: ((1 2) (3 4) (5 6)) ") +(invert '((2 1) (4 3) (6 5))) + + +;; ============ PROCEDURE ============ +;; NAME: vector-index +;; +;; DESC: +;; returns the zero-based index of the first +;; occurence of a parameter in a vector, or +;; -1 if there is no occurrence. +(define vector-index + (λ (needle haystack) + (cond + [ (null? needle) (display "Invalid Parameters") ] + [ (vector? haystack) (list-index needle (vector->list haystack)) ] + [ else (display "Invalid Parameters") ] ))) + +;; a helper function +;; PRECONDITION: haystack is a non-nested list (e.g. the result of vector->list) +(define list-index + (λ (needle haystack) + (if (null? haystack) + -1 + (if (equal? (car haystack) needle) + 0 + (if (equal? (list-index needle (cdr haystack)) -1) + -1 + (+ 1 (list-index needle (cdr haystack)))))))) + +;; ============ TEST CODE ============ +(newline) +(display "Testing (vector-index) ===================================") +(newline) + +(display "Expected output: 2 ") +(vector-index 3 #(1 2 3 4 5 6 7 8 9)) + +(display "Expected output: -1 ") +(vector-index 4 #(1 2 3)) + +(display "Expected output: -1 ") +(vector-index 3 #()) + + +;; ============ PROCEDURE ============ +;; NAME: count-occurrences +;; +;; DESC: +;; counts the occurrences of needle in haystack +(define count-occurrences + (λ (needle haystack) + (cond + [ (null? needle) (display "Error: nothing to search for") ] + [ (null? haystack) 0 ] + [ (list? (car haystack)) (+ (count-occurrences needle (car haystack)) (count-occurrences needle (cdr haystack))) ] + [ (equal? (car haystack) needle) (+ 1 (count-occurrences needle (cdr haystack))) ] + [ else (count-occurrences needle (cdr haystack)) ] ))) + +;; ============ TEST CODE ============ +(newline) +(display "Testing (count-occurrences) ==============================") +(newline) + +(display "Expected output: 10 ") +(count-occurrences 'a '(a b a c d (((((((((a))))))))) e f a b a a (d e) (a) c (a (a (a))))) + +(display "Expected output: 0 ") +(count-occurrences 'a '()) + +(display "Expected output: 1 ") +(count-occurrences 'a '(a)) + +;; ============ PROCEDURE ============ +;; NAME: compose +;; +;; DESC: +;; takes 1, 2, or 3 procedures and composes them, as specified by the equation: +;; (compose f g h) = (compose f (compose g h)) +(define compose + (λ funcs + (cond + [ (equal? (length funcs) 1) (car funcs) ] + [ (equal? (length funcs) 2) (λ (x) ((car funcs) ((cadr funcs) x))) ] + [ (equal? (length funcs) 3) (λ (x) ((car funcs) ((cadr funcs) ((caddr funcs) x)))) ] + [ else (display "Invalid parameters") ] ))) + +;; ============ TEST CODE ============ +(newline) +(display "Testing (compose) ========================================") +(newline) + +(display "Expected output: 1 ") +((compose car cdr cdr) '(0 2 1 3)) + +(display "Expected output: 1 ") +((compose car) '(1 2 3 4)) + +(display "Expected output: 1 ") +((compose car cdr) '(0 1 2 3)) + +(display "Expected output: 1 ") +((compose - -) 1) + +;; =========== END OF FILE ===========
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