lua: multi-return + unpack at call sites (+10 tests)

lib/lua/runtime.sx

@@ -169,3 +169,49 @@
     (if (= t nil) nil (let ((v (get t (str k)))) (if (= v nil) nil v)))))
 
 (define lua-set! (fn (t k v) (assoc t (str k) v)))
+
+(define
+  lua-multi?
+  (fn
+    (v)
+    (and
+      (= (type-of v) "list")
+      (> (len v) 0)
+      (= (first v) (quote lua-multi)))))
+
+(define
+  lua-first
+  (fn
+    (v)
+    (cond
+      ((lua-multi? v) (if (> (len v) 1) (nth v 1) nil))
+      (else v))))
+
+(define
+  lua-nth-ret
+  (fn
+    (v i)
+    (cond
+      ((lua-multi? v)
+        (let ((idx (+ i 1))) (if (< idx (len v)) (nth v idx) nil)))
+      (else (if (= i 0) v nil)))))
+
+(define
+  lua-pack-build
+  (fn
+    (vals i)
+    (cond
+      ((>= i (len vals)) (list))
+      ((= i (- (len vals) 1))
+        (let
+          ((last (nth vals i)))
+          (if (lua-multi? last) (rest last) (list last))))
+      (else (cons (nth vals i) (lua-pack-build vals (+ i 1)))))))
+
+(define
+  lua-pack-return
+  (fn
+    (vals)
+    (cond
+      ((= (len vals) 0) (list (quote lua-multi)))
+      (else (cons (quote lua-multi) (lua-pack-build vals 0))))))