;;;; The prelude's in-place slice algorithms.
;;;;
;;;; Every input here is chosen so that a wrong implementation passes nothing.
;;;; The sort input is unsorted, has duplicates, has negatives and has an odd
;;;; length, so a comparison with the wrong sense, an off-by-one that drops the
;;;; last element, and a swap that loses an equal key all show up. The second
;;;; sort is reverse-sorted, which is the worst case for insertion sort and the
;;;; case a no-op comparison would pass. The third sorts a *subslice* and then
;;;; prints the whole owning array: a slice is ptr+len into its owner, so the
;;;; five elements inside the range must be sorted and the three outside it
;;;; must be untouched. That last one is the property that dies silently if a
;;;; slice parameter ever starts being copied.

(defonce xs [7 i32])
(defonce ys [5 i32])
(defonce zs [8 i32])

(defn show [s [i32]] ()
  (dotimes [i (len s)]
    (when (> i 0) (print " "))
    (print (at s i)))
  (println ""))

(defn load-xs [] ()
  (set (at xs 0) 5)
  (set (at xs 1) -3)
  (set (at xs 2) 5)
  (set (at xs 3) 0)
  (set (at xs 4) 12)
  (set (at xs 5) -3)
  (set (at xs 6) 7))

(defn main [] i32
  (load-xs)
  (show (slice xs 0 (len xs)))                    ; 5 -3 5 0 12 -3 7

  ;; Reading the whole slice, before anything reorders it.
  (print (sum-i32 (slice xs 0 (len xs)))) (println "")            ; 23
  (print (match (min-of (slice xs 0 (len xs))) (Some v) v None 99))
  (println "")                                    ; -3
  (print (match (max-of (slice xs 0 (len xs))) (Some v) v None 99))
  (println "")                                    ; 12
  ;; First index, not the last: 5 appears at 0 and at 2.
  (print (match (index-of (slice xs 0 (len xs)) 5) (Some v) v None -1))
  (println "")                                    ; 0
  (print (match (index-of (slice xs 0 (len xs)) 4) (Some v) v None -1))
  (println "")                                    ; -1
  ;; An empty slice has no least element, and None is the answer.
  (print (match (min-of (slice xs 3 3)) (Some v) v None 99))
  (println "")                                    ; 99

  ;; Reverse of an odd-length slice: the middle element stays put.
  (reverse (slice xs 0 (len xs)))
  (show (slice xs 0 (len xs)))                    ; 7 -3 12 0 5 -3 5
  ;; And of a two-element one, the smallest case that can actually move.
  (reverse (slice xs 0 2))
  (show (slice xs 0 (len xs)))                    ; -3 7 12 0 5 -3 5

  (load-xs)
  (sort (slice xs 0 (len xs)))
  (show (slice xs 0 (len xs)))                    ; -3 -3 0 5 5 7 12

  ;; Reverse-sorted: the case a comparison that never fires would pass.
  (set (at ys 0) 5) (set (at ys 1) 4) (set (at ys 2) 3)
  (set (at ys 3) 2) (set (at ys 4) 1)
  (sort (slice ys 0 (len ys)))
  (show (slice ys 0 (len ys)))                    ; 1 2 3 4 5

  ;; A subslice, with the elements on both sides left alone.
  (set (at zs 0) 100) (set (at zs 1) 9) (set (at zs 2) -1)
  (set (at zs 3) 9) (set (at zs 4) 4) (set (at zs 5) 0)
  (set (at zs 6) 200) (set (at zs 7) 300)
  (sort (slice zs 1 6))
  (show (slice zs 0 (len zs)))                    ; 100 -1 0 4 9 9 200 300

  ;; Degenerate lengths must do nothing rather than run off an end.
  (sort (slice zs 0 0))
  (reverse (slice zs 0 0))
  (sort (slice zs 2 3))
  (reverse (slice zs 2 3))
  (show (slice zs 0 (len zs)))                    ; 100 -1 0 4 9 9 200 300

  ;; ── The short arities ──────────────────────────────────────────────
  ;; (slice a) and (slice a n) are (slice a 0 (len a)) and (slice a n (len a))
  ;; written out in the checker, so each line here is read against the
  ;; spelling above it that it stands for. A fixed array does not decay to a
  ;; slice at a call, so passing one to a function over [$t] is what these
  ;; exist for.
  (load-xs)
  (show (slice xs))                               ; 5 -3 5 0 12 -3 7
  (show (slice xs 4))                             ; 12 -3 7
  ;; Of a slice rather than of an array: the length is the slice's own, so
  ;; these index from where the previous one started, not from the array's 0.
  (show (slice (slice xs)))                       ; 5 -3 5 0 12 -3 7
  (show (slice (slice xs 2) 1))                   ; 0 12 -3 7

  ;; A literal array is nobody's named place, and it still slices: the two
  ;; lines the author hit are these, one sorting through the prelude's
  ;; generic [$t] sort and one over character literals.
  (sort (slice [6 2 4 9 1 9 4 5]))
  (let [a [6 2 4 9 1 9 4 5]]
    (sort (slice a))
    (show (slice a)))                             ; 1 2 4 4 5 6 9 9
  (let [cs [\I \N \S \E \R \T \I \O \N \S \O \R \T]]
    (sort (slice cs))
    (println (string (slice cs))))                ; EIINNOORRSSTT

  ;; ── Strings ────────────────────────────────────────────────────────
  ;; A string is ptr+len over bytes, so it indexes to a byte and slices to a
  ;; string viewing the same bytes. No copy, and no route through [u8].
  (let [s "insertion"]
    (print (at s 0)) (println "")                 ; 105
    (println (slice s))                           ; insertion
    (println (slice s 6))                         ; ion
    (println (slice s 0 6)))                      ; insert
  (println (slice "sorted" 2 4))                  ; rt
  0)