How to design a function that takes two Boolean parameters and returns true if either (or both) of the parameters are true?

Question

;Boolean b1 b2:

;#true & #true => #true

;#true & #false => #true

;#false & #false => #false

I kind of know how it works, but I don't know how to write it in Racket. I should have two parameters in a function, but how can I write that in Racket. Should it starts like

(define (either-true? b1 b2)

())

Answer 1

Other answers show that the body of either-true? could be just
(or b1 b2) or (if b1 #t b2) (or even (if b2 #t b1) )

A literal implementation of the "purpose" of either-true? could be:

(define (either-true? b1 b2) ;; Boolean Boolean -> Boolean
  ;; produce #t if either b1 or b2 is true, otherwise #f
  (cond
    [ b1 #t ]
    [ b2 #t ]
    [else #f ]))

In the Racket student languages, conditional forms (if, cond, or, etc) require their "question-expressions" to be Boolean values (#t or #f). Other Racket languages use the Scheme interpretation of any non-#f value as true in conditional contexts.

So yet another definition, using this interpretation of "truthiness", could be:

#lang racket

(define (either-true? b1 b2) ;; Any Any -> Any
  ;; produce #f if both b1 and b2 #f, otherwise a truthy value
  (findf values (list b1 b2)))

It's worth noting that, although (either-true? b1 b2) looks like (or b1 b2), there is a significant difference: or will not evaluate b2 if b1 is true; either-true? always evaluates both arguments. The difference can be seen by running:

#lang racket

(require math/number-theory)

(define (either-true? b1 b2)
  (or b1 b2))

(time (or           (prime? 7) (prime? (next-prime (expt 2 1000)))))
(time (either-true? (prime? 7) (prime? (next-prime (expt 2 1000)))))

Answer 2

(define (either-true? b1 b2) (if b1 #t b2))

also make sure you have both of these check-expects: (check-expect (either-true? #t #f) #t) (check-expect (either-true? #f #t) #t)

good luck with fundies 1 lol

Answer 3

Your either-true? exists already in Racket and is called or.

(define (either-true? b1 b2) (or b1 b2))

Or just do:

(define either-true? or)