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CS3L: Introduction to Symbolic Programming

CS3L: Introduction to Symbolic Programming. Summer 2008 Colleen Lewis colleenL@berkeley.edu. Lecture 12: Homework stuff and Accumulating Recursion. Today. I’m sick. I’m going home after lecture, but I’ll be online Homework Thurs: Bowling (Hwk11) due Monday

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CS3L: Introduction to Symbolic Programming

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  1. CS3L: Introduction to Symbolic Programming Summer 2008 Colleen Lewis colleenL@berkeley.edu Lecture 12: Homework stuff and Accumulating Recursion

  2. Today • I’m sick. • I’m going home after lecture, but I’ll be online • Homework • Thurs: Bowling (Hwk11) due Monday • Fri: Compress/occurs-in? (Hwk12) due Tuesday • Mon: Mini-project 2 due Wednesday • Testing the Bowling Program • Accumulating Recursion • Compressed • Occurs-in?

  3. Testing Bowling • Don’t start programming before you can calculate a bowling score by hand • Test with simple cases • ‘(10 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0) • The last frame is complicated!

  4. Accumulating Recursion (define (gather-evens sent) (cond ((empty? sent) ‘()) ((even? (first sent)) (se (first sent) (gather-evens (bf sent)))) (else (gather-evens (bf sent))))

  5. (se 2 (gather-evens‘( 3 4 5 6 )) (gather-evens‘( 4 5 6 )) (se 4 (gather-evens ‘( 5 6 )) (gather-evens ‘( 6 )) (se 6 (gather-evens ‘( )) > (gather-evens '(2 3 4 5 6)) (gather-evens ‘( 2 3 4 5 6 )) ‘() • (se 2 (se 4 (se 6 ‘()))) • (2 4 6)

  6. Accumulating Recursion (define (gather-evens evens-so-far sent) (cond ((empty? sent) evens-so-far) ((even? (first sent)) (gather-evens (se evens-so-far (first sent)) (bf sent))) (else (gather-evens evens-so-far (bf sent)))) (define (gather-evens sent) (cond ((empty? sent) ‘()) ((even? (first sent)) (se (first sent) (gather-evens (bf sent)))) (else (gather-evens (bf sent))))

  7. Final Version of gather-evens w/ Accumulating Recursion (define (gather-evens evens-so-far sent) (cond ((empty? sent) evens-so-far) ((even? (first sent)) (gather-evens (se evens-so-far (first sent)) (bf sent))) (else (gather-evens evens-so-far (bf sent))))

  8. Homework - Compressed • (0 0 0 0 1 0 0 0 0 1 1 1 1 1 1 1 1 1) • ( 4 0 1 4 0 9 1) • (0 1 0 1) • (0 1 0 1)

  9. Homework - Occurs-in? • (occurs-in? 'abc 'abcde) #t • (occurs-in? 'abc 'xyabc) #t • (occurs-in? 'ab 'axbc) #f • (occurs-in? 'abc 'xy) #f • This is not an exhaustive list!!!

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