forth: DO/LOOP/+LOOP/I/J/LEAVE + return stack words (+16)

lib/forth/runtime.sx

@@ -449,4 +449,42 @@
             (> n 0)
             (for-each (fn (_) (forth-emit-str s " ")) (range 0 n))))))
     (forth-def-prim! state "BL" (fn (s) (forth-push s 32)))
+    (forth-def-prim! state "I" (fn (s) (forth-push s (forth-rpeek s))))
+    (forth-def-prim!
+      state
+      "J"
+      (fn (s) (forth-push s (nth (get s "rstack") 2))))
+    (forth-def-prim! state ">R" (fn (s) (forth-rpush s (forth-pop s))))
+    (forth-def-prim! state "R>" (fn (s) (forth-push s (forth-rpop s))))
+    (forth-def-prim! state "R@" (fn (s) (forth-push s (forth-rpeek s))))
+    (forth-def-prim!
+      state
+      "2>R"
+      (fn
+        (s)
+        (let
+          ((b (forth-pop s)) (a (forth-pop s)))
+          (forth-rpush s a)
+          (forth-rpush s b))))
+    (forth-def-prim!
+      state
+      "2R>"
+      (fn
+        (s)
+        (let
+          ((b (forth-rpop s)) (a (forth-rpop s)))
+          (forth-push s a)
+          (forth-push s b))))
+    (forth-def-prim!
+      state
+      "2R@"
+      (fn
+        (s)
+        (let
+          ((rs (get s "rstack")))
+          (when
+            (< (len rs) 2)
+            (forth-error s "return stack underflow"))
+          (forth-push s (nth rs 1))
+          (forth-push s (nth rs 0)))))
     state))