rose-ash/lib/erlang/lists-ext.sx

;; lib/erlang/lists-ext.sx — extra `lists` module BIFs.
;;
;; Loaded AFTER runtime.sx so the BIF registry + transpile helpers
;; (er-mk-cons, er-lt?, er-equal?, er-bool, er-truthy?, er-apply-fun,
;; er-bif-arg1, er-mk-error-marker, er-mk-atom, er-cons?, er-nil?) and
;; runtime's er-register-pure-bif! are all in scope. Registrations run
;; at load time and persist in the global er-bif-registry cell.
;;
;; Edit-tool note: the sx-tree write tools raise yojson "Expected
;; string, got null" in this worktree, so new lists BIFs land here (a
;; fresh file) rather than as in-place edits to the ~1900-line
;; transpile.sx. Same separate-file pattern the VM dispatcher already
;; uses (lib/erlang/vm/dispatcher.sx).

;; ── cons <-> SX-list bridges ──────────────────────────────────────
(define
  er-cons->sxlist
  (fn (lst)
    (cond
      (er-nil? lst) (list)
      (er-cons? lst) (cons (get lst :head) (er-cons->sxlist (get lst :tail)))
      :else (raise (er-mk-error-marker (er-mk-atom "badarg"))))))

(define
  er-sxlist->cons
  (fn (xs)
    (if (= (len xs) 0)
      (er-mk-nil)
      (er-mk-cons (first xs) (er-sxlist->cons (rest xs))))))

;; ── merge sort over SX lists (stable) ─────────────────────────────
(define
  er-ext-take
  (fn (xs n)
    (if (or (= n 0) (= (len xs) 0))
      (list)
      (cons (first xs) (er-ext-take (rest xs) (- n 1))))))

(define
  er-ext-drop
  (fn (xs n)
    (if (or (= n 0) (= (len xs) 0))
      xs
      (er-ext-drop (rest xs) (- n 1)))))

;; le? returns a truthy value (Erlang bool atom or SX bool) iff a
;; should sort at-or-before b. Taking from the left half first on a
;; true result keeps the sort stable.
(define
  er-ext-merge
  (fn (a b le?)
    (cond
      (= (len a) 0) b
      (= (len b) 0) a
      (er-truthy? (le? (first a) (first b)))
        (cons (first a) (er-ext-merge (rest a) b le?))
      :else (cons (first b) (er-ext-merge a (rest b) le?)))))

(define
  er-ext-msort
  (fn (xs le?)
    (if (<= (len xs) 1)
      xs
      (let ((mid (quotient (len xs) 2)))
        (er-ext-merge
          (er-ext-msort (er-ext-take xs mid) le?)
          (er-ext-msort (er-ext-drop xs mid) le?)
          le?)))))

;; Full Erlang term order. The shared er-lt? (transpile.sx) only
;; deep-compares numbers/atoms/strings and otherwise falls back to a
;; coarse type rank — so any two tuples (or two lists) compare as
;; order-equal there. er-ext-lt? adds the missing structural cases:
;; tuples by arity then elementwise, lists elementwise with a shorter
;; proper prefix sorting first. Cross-type cases delegate to er-lt?.
(define
  er-ext-lt-seq
  (fn (ea eb i)
    (cond
      (>= i (len ea)) false
      (er-ext-lt? (nth ea i) (nth eb i)) true
      (er-ext-lt? (nth eb i) (nth ea i)) false
      :else (er-ext-lt-seq ea eb (+ i 1)))))

(define
  er-ext-lt?
  (fn (a b)
    (cond
      (and (er-tuple? a) (er-tuple? b))
        (let ((ea (get a :elements)) (eb (get b :elements)))
          (cond
            (< (len ea) (len eb)) true
            (> (len ea) (len eb)) false
            :else (er-ext-lt-seq ea eb 0)))
      (and (er-cons? a) (er-cons? b))
        (cond
          (er-ext-lt? (get a :head) (get b :head)) true
          (er-ext-lt? (get b :head) (get a :head)) false
          :else (er-ext-lt? (get a :tail) (get b :tail)))
      (and (er-nil? a) (er-cons? b)) true
      (and (er-cons? a) (er-nil? b)) false
      (and (er-nil? a) (er-nil? b)) false
      :else (er-lt? a b))))

;; Default Erlang term order: a =< b  ==  not (b < a).
(define
  er-ext-term-le
  (fn (a b) (er-bool (not (er-ext-lt? b a)))))

;; ── lists:sort/1, lists:sort/2 ────────────────────────────────────
(define
  er-bif-lists-sort
  (fn (vs)
    (cond
      (= (len vs) 1)
        (er-sxlist->cons
          (er-ext-msort (er-cons->sxlist (nth vs 0)) er-ext-term-le))
      (= (len vs) 2)
        (let ((f (nth vs 0)) (lst (nth vs 1)))
          (er-sxlist->cons
            (er-ext-msort
              (er-cons->sxlist lst)
              (fn (a b) (er-apply-fun f (list a b))))))
      :else (error "Erlang: lists:sort: wrong arity"))))

;; ── lists:usort/1 (sort then drop adjacent term-equal dups) ───────
(define
  er-ext-dedup
  (fn (xs)
    (cond
      (= (len xs) 0) (list)
      (= (len xs) 1) xs
      (er-equal? (first xs) (nth xs 1)) (er-ext-dedup (rest xs))
      :else (cons (first xs) (er-ext-dedup (rest xs))))))

(define
  er-bif-lists-usort
  (fn (vs)
    (let ((lst (er-bif-arg1 vs "lists:usort")))
      (er-sxlist->cons
        (er-ext-dedup
          (er-ext-msort (er-cons->sxlist lst) er-ext-term-le))))))

;; ── register ──────────────────────────────────────────────────────
;; Hook into er-register-builtin-bifs! rather than registering once:
;; the registry can be reset + rebuilt mid-run (tests/runtime.sx does
;; this), and a plain one-shot registration would be wiped. Wrapping
;; the rebuild fn means these BIFs are re-added on every reset.
(define er-ext-lists-register!
  (fn ()
    (er-register-pure-bif! "lists" "sort" 1 er-bif-lists-sort)
    (er-register-pure-bif! "lists" "sort" 2 er-bif-lists-sort)
    (er-register-pure-bif! "lists" "usort" 1 er-bif-lists-usort)))

(define er-ext-prev-register-builtins er-register-builtin-bifs!)
(define er-register-builtin-bifs!
  (fn ()
    (er-ext-prev-register-builtins)
    (er-ext-lists-register!)))

;; register into the currently-live registry too
(er-ext-lists-register!)