Just pushed the tail recursive non-recur and now the other one doesn't stack overflow with a stack of 512k.

clj -J-Xss512k -Sdeps '{:deps {meander/epsilon {:local/root "."}}}' -e "(require '[meander.epsilon :as m])  (defn z [] (m/rewrite {} (loop* [?seq (clojure.core/seq ?xs) ?chunk nil ?chunkn 0 ?i 0] (if (clojure.lang.Numbers/lt ?i ?chunkn) (let* [(m/and ?sym (m/app always-meta {:tag  ?tag :type ?type})) (.nth ?chunk ?i)] (do ?body (recur ?seq ?chunk ?chunkn (clojure.lang.Numbers/unchecked_inc ?i)))) (let* [?as (clojure.core/seq ?seq)] (if ?as (let* [?bs ?as] (if (clojure.core/chunked-seq? ?bs) (let* [?cs (clojure.core/chunk-first ?bs)] (recur (clojure.core/chunk-rest ?bs) ?cs (clojure.lang.RT/intCast (clojure.lang.RT/count ?cs)) (clojure.lang.RT/intCast 0))) (let* [?sym (clojure.core/first ?bs)] (do ?body (recur (clojure.core/next ?bs) nil 0 0))))))))) (foreach ~(or ?type ?tag) ?sym ?xs (m/app inner-form ?body))))"

I was hoping something like kondo would give a warning about this. But it doesn't. If anyone knows a tool that can lint non-recur tail recursion, that would be great to find.

We could probably trampoline walk/prewalk/postwalk and get our stack size much smaller. Obviously with a macroexpansion performance hit.

As I'm looking at things, walk seems to be the thing that grows our stack most often. So if we want to reduce it, making some walk that didn't grow the stack would definitely be the approach we should take. Just fyi, default stack of 32bit is 320k default for 64bit is 1024k.

Thanks for looking at this!

We could trade stack for heap and use a zipper approach but that implies filling in blanks for the usual zipper stuff.

I think ref substitution is where we end up eating the most stack.