Problem Set 6

Language: Intermediate Student with lambda
Due: 11:59 PM Thursday, Feb. 17

1 Practice Abstracting

The retrieved file contains the data definitions for person and database, as well as definitions and tests of the create-database and create-database-from-list functions. Add your code to this file and submit the whole thing when you’re done.

Note there is a slight change from Problem Set 4 in the definition of create-database: the relative order of the function’s parameters is flipped, making the person argument the first argument instead of the second. With this change, the definition of create-database-from-list closely resembles the following definition of sum.

; sum: list-of-number -> number

; Produces the sum of the given numbers

(define (sum lon)

(cond [(empty? lon) 0]

[(cons? lon) (+ (first lon) (sum (rest lon)))]))

(check-expect (sum empty) 0)

(check-expect (sum (list 2 5 -1 3)) 9)

Abstract the common parts of these definitions of create-database-from-list and sum into a new function called reduce. Redefine create-database-from-list and sum in terms of reduce.

2 Practice with map and filter

Use map and filter, along with lambda, to define the following functions.

; pts-north : posn list-of-posn -> list-of-posn

; returns the posns from lop that are north of p,

; that is, whose y-coordinate is greater than p's y-coordinate

(define (pts-north p lop) ---)

; build-straight-line : num list-of-number -> list-of-posn

; returns a list of posns where the x-coordinate is n and

; the y-coordinate is a number in lon

; e.g., (build-straight-line 2 (list 1 2 3))

; should be (list (make-posn 2 1) (make-posn 2 2) (make-posn 2 3))

(define (build-straight-line n lon) ---)