In Scala you can do something like this:
def times[A](item: A, number: Int): List[A] = number match {
case n if n <= 0 => Nil // Nil = '()
case _ =>
// equivalent to [_ (cons item (times item (- number 1)))]
item :: times(item, number - 1)
}
Is it possible to do something like this using Racket's match form? I couldn't find it in the documentation
For those not familiar with Scala, the first case matches if the number is equal to or less than 0, the second case is just a wildcard that matches everything else
in other words, what would I write in the ??? spot to achieve similar functionality to what I described above?
(define (times item number)
(match number
[??? '()]
[_ (cons item (times item (- number 1)))]))
Racket's match has an optional #:when clause that lets you write this almost exactly as you did in Scala:
(define (times item number)
(match number
[n #:when (<= n 0) '()]
[_ (cons item (times item (- number 1)))]))
I think that answers your question, literally. But more idiomatic Racket would be to use cond for something like this -- where it's a simple conditional test and you don't need any destructuring:
(define (times item number)
(cond [(<= number 0) '()]
[else (cons item (times item (- number 1)))]))
Although I'd probably flip the arms:
(define (times item number)
(cond [(positive? number) (cons item (times item (- number 1)))]
[else '()]))
Of course for something this simple you could use if:
(define (times item number)
(if (positive? number)
(cons item (times item (- number 1)))
'()))
However I've grown to prefer using cond, as the Racket style guide recommends.