adding a FIXME to this; tracked in #18

src/regression-tests/goals/seq-cont/alt-ret-tuple.pml

@@ -11,18 +11,28 @@ fun snd (_, x) = x
 fun max (a, b) = if a > b then a else b
 
 (* fib that alternates between returning normally or using its escape cont *)
-fun fib n k = (case n
-  of 0 => altRet (n, (0, 1), k)
-   | 1 => altRet (n, (1, 1), k)
-   | _ => let
+(* FIXME: if you change the `if` below into
+
+    case n
+      of 0 => altRet (n, (0, 1), k)
+       | 1 => altRet (n, (1, 1), k)
+       | _ => let ...
+
+    Then you get the wrong answer, but only when using hybridstacks.
+    It's not in the ASM code, since the generated ASM is identical to
+    that of segmented stacks. So there must be something wrong in the RTS.
+  *)
+fun fib n k =
+  if n <= 1
+    then altRet (n, (n, 1), k)
+    else let
         val left = Cont.callec (fib (n-1))
         val right = Cont.callec (fib (n-2))
         val ans = fst left + fst right
         val depth = max (snd left, snd right) + 1
       in
         altRet (n, (ans, depth), k)
       end
-  (* end case *))
 
 val i2s = Int.toString