Kilian Sprotte wrote:
although I might become an iterate developer one day,
I don't know whether this comment relates to your proposal to find the "twice previous bug". Maybe you shouldn't start with the hardest bug. There are 2 other issues:
- make Iterate for num accept the exact same keywords as Loop e.g. Loop for downfrom to (presumably easiest) - prefix clause bug e.g. cannot define both clauses (foo x) and (foo x bar y). (needs correct implementation of a trie)
I took another look at the "twice previous bug" the other day (despite having -09 time). My current suspicion is that the code breaks some invariant. The previous-code-info keeps a ref and LAST to remember the for-clause's body. When PREVIOUS is seen, that body is surrounded with (setq #:previous-var xyz) and (setq previous-var zyx) with destructive modifications of list structure. But doing so, the ref and LAST pointers must be updated as well, for a second PREVIOUS splice to work. Maybe that's the invariant that gets violated?
(iter (repeat 3) (for (values a b) = (floor 5 2)) (for p-a previous a) (for p-b previous b) (collect (list a b p-a p-b)))
Regards, Jorg Hohle.