apl: Phase 3 catenate , and first-axis — 59/59 tests green

Add apl-catenate (dyadic ,, last-axis join, scalar promotion) and
apl-catenate-first (first-axis join, row-major append). 9 new tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/apl/runtime.sx

@@ -606,3 +606,58 @@
                     ((old-c-last (apl-safe-mod (+ c-last rot) last-dim)))
                     (nth ravel (+ flat (- old-c-last c-last))))))
               (range 0 n))))))))
+
+(define
+  apl-catenate
+  (fn
+    (a b)
+    (let
+      ((a-s (if (scalar? a) (list 1) (get a :shape)))
+        (b-s (if (scalar? b) (list 1) (get b :shape)))
+        (a-r (get a :ravel))
+        (b-r (get b :ravel)))
+      (let
+        ((a-last (last a-s)) (prefix (take a-s (- (len a-s) 1))))
+        (let
+          ((new-shape (append prefix (list (+ a-last (last b-s)))))
+            (a-strides (apl-strides a-s))
+            (b-strides (apl-strides b-s)))
+          (let
+            ((new-size (reduce * 1 new-shape))
+              (new-strides (apl-strides new-shape)))
+            (make-array
+              new-shape
+              (map
+                (fn
+                  (new-flat)
+                  (let
+                    ((new-coords (apl-flat->multi new-flat new-shape new-strides)))
+                    (let
+                      ((last-c (last new-coords))
+                        (prefix-c (take new-coords (- (len new-coords) 1))))
+                      (if
+                        (< last-c a-last)
+                        (nth
+                          a-r
+                          (apl-multi->flat
+                            (append prefix-c (list last-c))
+                            a-strides))
+                        (nth
+                          b-r
+                          (apl-multi->flat
+                            (append prefix-c (list (- last-c a-last)))
+                            b-strides))))))
+                (range 0 new-size)))))))))
+
+(define
+  apl-catenate-first
+  (fn
+    (a b)
+    (let
+      ((a-s (if (scalar? a) (list 1) (get a :shape)))
+        (b-s (if (scalar? b) (list 1) (get b :shape)))
+        (a-r (get a :ravel))
+        (b-r (get b :ravel)))
+      (make-array
+        (cons (+ (first a-s) (first b-s)) (rest a-s))
+        (append a-r b-r)))))

lib/apl/tests/structural.sx

@@ -322,4 +322,70 @@
     (apl-rotate-first
       (apl-scalar 1)
       (make-array (list 2 3) (list 1 2 3 4 5 6))))
-  (list 4 5 6 1 2 3))
+  (list 4 5 6 1 2 3))
+
+(apl-test
+  "cat v,v ravel"
+  (rv
+    (apl-catenate
+      (make-array (list 3) (list 1 2 3))
+      (make-array (list 2) (list 4 5))))
+  (list 1 2 3 4 5))
+
+(apl-test
+  "cat v,v shape"
+  (sh
+    (apl-catenate
+      (make-array (list 3) (list 1 2 3))
+      (make-array (list 2) (list 4 5))))
+  (list 5))
+
+(apl-test
+  "cat scalar,v"
+  (rv (apl-catenate (apl-scalar 99) (make-array (list 3) (list 1 2 3))))
+  (list 99 1 2 3))
+
+(apl-test
+  "cat v,scalar"
+  (rv (apl-catenate (make-array (list 3) (list 1 2 3)) (apl-scalar 99)))
+  (list 1 2 3 99))
+
+(apl-test
+  "cat matrix last-axis shape"
+  (sh
+    (apl-catenate
+      (make-array (list 2 3) (list 1 2 3 4 5 6))
+      (make-array (list 2 2) (list 7 8 9 10))))
+  (list 2 5))
+
+(apl-test
+  "cat matrix last-axis ravel"
+  (rv
+    (apl-catenate
+      (make-array (list 2 3) (list 1 2 3 4 5 6))
+      (make-array (list 2 2) (list 7 8 9 10))))
+  (list 1 2 3 7 8 4 5 6 9 10))
+
+(apl-test
+  "cat-first v,v shape"
+  (sh
+    (apl-catenate-first
+      (make-array (list 3) (list 1 2 3))
+      (make-array (list 2) (list 4 5))))
+  (list 5))
+
+(apl-test
+  "cat-first matrix shape"
+  (sh
+    (apl-catenate-first
+      (make-array (list 2 3) (list 1 2 3 4 5 6))
+      (make-array (list 3 3) (list 11 12 13 14 15 16 17 18 19))))
+  (list 5 3))
+
+(apl-test
+  "cat-first matrix ravel"
+  (rv
+    (apl-catenate-first
+      (make-array (list 2 3) (list 1 2 3 4 5 6))
+      (make-array (list 3 3) (list 11 12 13 14 15 16 17 18 19))))
+  (list 1 2 3 4 5 6 11 12 13 14 15 16 17 18 19))