; we extend the array module, now that we have strings
(defmodule Array
  (doc range "creates an array from `start` to `end` with `step` between them
(the elements must support `<`, `<=`, `>=`, and `to-int`).

It returns a `Result.Success` if the input was right, and a `Result.Error` if
the input given was wrong, containing an error message.")
  (defn range [start end step]
    (cond
      (= step (zero))
        (Result.Error @"`Array.range` cannot be called with step size `0`.")
      (and (< start end) (< step (zero)))
        (Result.Error @"`Array.range` cannot be called with a step size `< 0` and `start < end`.")
      (and (> start end) (> step (zero)))
        (Result.Error @"`Array.range` cannot be called with a step size `> 0` and `start > end`.")
      (let-do [x (allocate (Int.inc (Int.abs (to-int (/ (- end start) step)))))
               e start
               i 0
               op (if (< start end) <= >=)]
        (while (op e end)
          (do
            (aset! &x i e)
            (set! i (Int.inc i))
            (set! e (+ e step))))
        (Result.Success x))))

  (doc range-or-default "is a version of [`range`](#range) that returns an empty
array on failure.")
  (defn range-or-default [start end step]
    (Result.from-success (range start end step) []))
)