apl: ? roll/random + apl-rng-seed! (+4 tests)

apl-rng-state global mutable LCG.
apl-rng-seed! for deterministic tests.
apl-rng-next! advances state.
apl-roll: monadic ?N returns scalar in 1..N (apl-io-relative).

apl-monadic-fn dispatches "?" → apl-roll.

apl-run "?10" → 8 (with seed 42)
apl-run "?100" → in 1..100

lib/apl/runtime.sx

@@ -1004,6 +1004,28 @@
         (some (fn (c) (= c 0)) codes)
         (some (fn (c) (= c (nth e 1))) codes)))))
 
+(define apl-rng-state 12345)
+
+(define apl-rng-seed! (fn (s) (set! apl-rng-state s)))
+
+(define
+  apl-rng-next!
+  (fn
+    ()
+    (begin
+      (set!
+        apl-rng-state
+        (mod (+ (* apl-rng-state 1103515245) 12345) 2147483648))
+      apl-rng-state)))
+
+(define
+  apl-roll
+  (fn
+    (arr)
+    (let
+      ((n (if (scalar? arr) (first (get arr :ravel)) (first (get arr :ravel)))))
+      (apl-scalar (+ apl-io (mod (apl-rng-next!) n))))))
+
 (define
   apl-cartesian
   (fn

lib/apl/tests/pipeline.sx

@@ -359,3 +359,24 @@
   "inline-assign in dfn: f ← {x + x ← ⍵} ⋄ f 8 → 16"
   (mkrv (apl-run "f ← {x + x ← ⍵} ⋄ f 8"))
   (list 16))
+
+(begin (apl-rng-seed! 42) nil)
+
+(apl-test
+  "?10 with seed 42 → 8 (deterministic)"
+  (mkrv (apl-run "?10"))
+  (list 8))
+
+(apl-test "?10 next call → 5" (mkrv (apl-run "?10")) (list 5))
+
+(apl-test
+  "?100 stays in range"
+  (let ((v (first (mkrv (apl-run "?100"))))) (and (>= v 1) (<= v 100)))
+  true)
+
+(begin (apl-rng-seed! 42) nil)
+
+(apl-test
+  "?10 with re-seed 42 → 8 (reproducible)"
+  (mkrv (apl-run "?10"))
+  (list 8))

lib/apl/transpile.sx

@@ -39,6 +39,7 @@
       ((= g "⊖") apl-reverse-first)
       ((= g "⍋") apl-grade-up)
       ((= g "⍒") apl-grade-down)
+      ((= g "?") apl-roll)
       ((= g "⎕FMT") apl-quad-fmt)
       ((= g "⎕←") apl-quad-print)
       (else (error "no monadic fn for glyph")))))