List Motions

CSC 151 - Functional Problem Solving

Leah Perlmutter | Fall 2024

Agenda for Today

1. Announcements
2. List Motions
3. Lab
4. Quiz

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Announcements

Announcements

• Leah not doing so well because somebody I care about lost a family member this week
• Setting expectations for evening tutoring sessions

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List Motions

• nested pair structure of a list
• Self check 1 (demo code on following slides)

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(test-case "positive edge case: replace first element"

equal?

(list 999 2 3)

(lambda ()

(replace-first 9 999 (list 9 2 3))))

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(test-case "negative case: replace something not in the original list"

equal?

(list 1 2 3)

(lambda ()

(replace-first 9 999 (list 1 2 3))))

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(test-case "negative edge case: empty list"

equal?

(list)

(lambda ()

(replace-first 9 999 (list))))

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(define replace-first

(lambda (x y lst)

(match lst

[null null]

[(cons head tail)

(if (equal? head x)

(cons y tail)

(cons head (replace-first x y tail)))])))

;[(cons x tail)

; (cons y tail)]

;[(cons head tail)

; (cons head (replace-first x y tail))])))

; (cons z (replace-first x y tail))])))

;; Hypotheses

;; on line 12, we can't cons z, it's undefined

;; on line 9, x is not what we think it is

;; on line 9, x is being locally rebound

;; line 9 is no the right way to make sure head is x

;; we could use cond instead

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Before we begin

• Suggested Ice Breaker:
• What is a really good or really bad food you ate this week?

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Lab time!

Lab Tips

• Every recursive function has
• Base Case
• solve the whole problem in one step
• Recursive Case
• make the problem smaller and recur
• Think Before You Code!
• Use mini-whiteboards or a piece of paper to sketch out a plan!

End of lab (before quiz)

• 5 minutes left -- make a plan to finish your lab exercises!
• Before submitting, make a comment in your lab code saying how far you got through the exercises
• To prepare for the quiz, log out of your lab computer and put away everything except a writing implement (pencil and eraser recommended)

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Before the quiz

• Please log out of your lab computer and put away everything except a writing implement (pencil and eraser recommended)
• You have 15 minutes for the quiz, modified by any accommodations that you have talked with me about
• When finished, hand it in at the front of the room
• You may leave when finished
• If you have to talk to Prof. Perlmutter, we can go outside

As always:

• check course website for assignments and due dates
• When you go, put note cards back in bin if you have not already

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Quiz time

Quiz Clarification

• Quiz goes until 4:00 (we started late)

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