kernel: append + reverse + 11 tests [nothing]

Variadic append concatenates lists; reverse is unary. 307 tests total.

lib/kernel/runtime.sx

@@ -490,6 +490,48 @@
     "pair?"
     (fn (v) (and (list? v) (> (length v) 0)))))
 
+(define knl-append-step
+  (fn (xs ys)
+    (cond
+      ((or (nil? xs) (= (length xs) 0)) ys)
+      (:else (cons (first xs) (knl-append-step (rest xs) ys))))))
+
+(define knl-all-lists?
+  (fn (xs)
+    (cond
+      ((or (nil? xs) (= (length xs) 0)) true)
+      ((list? (first xs)) (knl-all-lists? (rest xs)))
+      (:else false))))
+
+(define knl-append-all
+  (fn (lists)
+    (cond
+      ((or (nil? lists) (= (length lists) 0)) (list))
+      ((= (length lists) 1) (first lists))
+      (:else
+        (knl-append-step (first lists)
+                         (knl-append-all (rest lists)))))))
+
+(define kernel-append-applicative
+  (kernel-make-primitive-applicative
+    (fn (args)
+      (cond
+        ((knl-all-lists? args) (knl-append-all args))
+        (:else (error "append: all arguments must be lists"))))))
+
+(define knl-reverse-step
+  (fn (xs acc)
+    (cond
+      ((or (nil? xs) (= (length xs) 0)) acc)
+      (:else (knl-reverse-step (rest xs) (cons (first xs) acc))))))
+
+(define kernel-reverse-applicative
+  (knl-unary-app "reverse"
+    (fn (xs)
+      (cond
+        ((not (list? xs)) (error "reverse: argument must be a list"))
+        (:else (knl-reverse-step xs (list)))))))
+
 (define kernel-not-applicative (knl-unary-app "not" (fn (v) (not v))))
 
 (define kernel-eq?-applicative (knl-bin-app "eq?" (fn (a b) (= a b))))
@@ -816,7 +858,9 @@
       (kernel-env-bind! env "map"    kernel-map-applicative)
       (kernel-env-bind! env "filter" kernel-filter-applicative)
       (kernel-env-bind! env "reduce" kernel-reduce-applicative)
-      (kernel-env-bind! env "apply"  kernel-apply-applicative)
+      (kernel-env-bind! env "apply"   kernel-apply-applicative)
+      (kernel-env-bind! env "append"  kernel-append-applicative)
+      (kernel-env-bind! env "reverse" kernel-reverse-applicative)
       (kernel-env-bind! env "not" kernel-not-applicative)
       (kernel-env-bind! env "make-encapsulation-type"
                             kernel-make-encap-type-applicative)

lib/kernel/tests/standard.sx

@@ -415,4 +415,31 @@
     (ks-eval "(apply + 5)"))
   :raised)
 
+;; ── append / reverse ────────────────────────────────────────────
+(ks-test "append: two lists"
+  (ks-eval "(append (list 1 2) (list 3 4))") (list 1 2 3 4))
+(ks-test "append: three lists"
+  (ks-eval "(append (list 1) (list 2) (list 3))") (list 1 2 3))
+(ks-test "append: empty list"
+  (ks-eval "(append)") (list))
+(ks-test "append: one list"
+  (ks-eval "(append (list 1 2 3))") (list 1 2 3))
+(ks-test "append: empty + nonempty"
+  (ks-eval "(append (list) (list 1 2))") (list 1 2))
+(ks-test "append: nonempty + empty"
+  (ks-eval "(append (list 1 2) (list))") (list 1 2))
+(ks-test "append: error on non-list"
+  (guard (e (true :raised))
+    (ks-eval "(append (list 1) 5)"))
+  :raised)
+
+(ks-test "reverse: four elements"
+  (ks-eval "(reverse (list 1 2 3 4))") (list 4 3 2 1))
+(ks-test "reverse: empty"
+  (ks-eval "(reverse (list))") (list))
+(ks-test "reverse: single"
+  (ks-eval "(reverse (list 99))") (list 99))
+(ks-test "reverse: double reverse is identity"
+  (ks-eval "(reverse (reverse (list 1 2 3)))") (list 1 2 3))
+
 (define ks-tests-run! (fn () {:total (+ ks-test-pass ks-test-fail) :passed ks-test-pass :failed ks-test-fail :fails ks-test-fails}))

plans/kernel-on-sx.md

@@ -161,6 +161,7 @@ The motivation is that SX's host `make-env` family is registered only in HTTP/si
 
 ## Progress log
 
+- 2026-05-11 — `append` (variadic) and `reverse`. Append concatenates any number of lists; empty `(append)` returns `()`. Reverse is unary. 11 new tests. chisel: nothing (textbook list ops). 307 tests total.
 - 2026-05-11 — `apply` combinator. `(apply F (list V1 V2 V3))` ≡ `(F V1 V2 V3)` but with the argument list constructed at runtime. Implementation: unwrap an applicative F to its underlying operative, then `kernel-combine` it with the values — skipping the auto-eval pass since args are already values. For a bare operative F, pass through directly. 7 new tests. chisel: shapes-reflective. The unwrap-then-combine pattern is universal across reflective Lisps and should be in the `combiner.sx` API alongside the existing wrap/unwrap pair: `refl-apply F ARGS DYN-ENV` is the third API entry needed for higher-order composition. 296 tests total.
 - 2026-05-11 — `map` / `filter` / `reduce` list combinators. Required adding `kernel-make-primitive-applicative-with-env` to `eval.sx`: standard primitive applicatives drop dyn-env, but combinators that re-enter the evaluator (calling user-supplied functions on each element) need it. The three combinators use `kernel-combine` directly with the captured dyn-env. 10 new tests covering map/filter/reduce on numbers, empty lists, closures, and list construction. chisel: shapes-reflective. The "primitive applicatives split into two flavours — env-blind and env-aware" finding goes into the proposed `lib/guest/reflective/combiner.sx` API. Every reflective Lisp must distinguish "I just need values" from "I need to re-enter evaluation" — the with-env constructor pair is universal. 289 tests total.
 - 2026-05-11 — Variadic `+ - * /` and chained `< > <=? >=?`. `(+ 1 2 3)` = 6, `(+)` = 0, `(+ 7)` = 7. `(- 10 1 2 3)` = 4 (left fold); single-arg `-` negates. `(* 1 2 3 4)` = 24, `(*)` = 1. Chained comparison: `(< 1 2 3)` ≡ `(< 1 2) ∧ (< 2 3)`. Implementation: `knl-fold-app` for n-ary fold with zero-arity identity and one-arity special-case; `knl-chain-cmp` for chained boolean. 19 new tests. chisel: nothing (mechanical extension of existing arithmetic primitives). 279 tests total.