forth: SP@ / SP! (+4; Hayes 174/590)

lib/forth/tests/test-phase4.sx

@@ -171,6 +171,24 @@
       ((r (forth-run "1000 2 ACCEPT")))
       (let ((stk (nth r 2))) (forth-p4-assert "ACCEPT empty buf -> 0" (list 0) stk)))))
 
+(define
+  forth-p4-sp-tests
+  (fn
+    ()
+    (forth-p4-check-top "SP@ returns depth (0)" "SP@" 0)
+    (forth-p4-check-top
+      "SP@ after pushes"
+      "1 2 3 SP@ SWAP DROP SWAP DROP SWAP DROP"
+      3)
+    (forth-p4-check-stack-size
+      "SP! truncates"
+      "1 2 3 4 5 2 SP!"
+      2)
+    (forth-p4-check-top
+      "SP! leaves base items intact"
+      "1 2 3 4 5 2 SP!"
+      2)))
+
 (define
   forth-p4-base-tests
   (fn
@@ -227,6 +245,7 @@
     (forth-p4-char-tests)
     (forth-p4-key-accept-tests)
     (forth-p4-base-tests)
+    (forth-p4-sp-tests)
     (dict
       "passed"
       forth-p4-passed