Do you mean this?
#lang racket
(require rackunit)
;; Nat Nat *-> [Listof Nat]
;; which of the
(define (same-parity x . xs)
(cons x (filter (λ (o) (or (and (even? x) (even? o)) (and (odd? x)
(odd? o)))) xs)))
(check-equal? (same-parity 1 2 3 4 5 6 7) '(1 3 5 7))
(check-equal? (same-parity 2 3 4 5 6 7) '(2 4 6))
On Jul 20, 2010, at 9:36 AM, Martin DeMello wrote:
By way of a puzzle, I've been trying to solve SICP exercise 2.20
----------------------------
Using the (define (f x . args)) notation, write a procedure
"same-parity" that takes one or more integers and returns a list of
all the arguments that have the same even-odd parity as the first
argument. For example,
(same-parity 1 2 3 4 5 6 7)
(1 3 5 7)
(same-parity 2 3 4 5 6 7)
(2 4 6)
----------------------------
using "straight recursion", that is, without using any `let` or
`define` constructs. Still not managed to find the trick that will
tack on the first argument as the head of the list. Anyone have a
hint?
martin
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