A recur from an arm of a match over an enum is in tail position, and a session's blind spot for macros an expansion defines is recorded

TODO.org

@@ -90,6 +90,12 @@ expansion that defines a macro re-runs the expander. =~~@x= is refused. There is
 no =,',x=, since =quote= takes a symbol, and a macro defined by an expansion is
 not exported from a package. docs/BUILT.md, "Quasiquote runs before the walk".
 
+** TODO A session does not remember a macro that an expansion defined
+=Session.own_macros= reads =defmacro= heads off the forms as sent, so after
+=(defsquare sq)= is evaluated the session's next form cannot call =sq=. A build
+sees the whole file and can. The fix is collecting from the expanded forms,
+which =Load.program= does not hand back.
+
 ** DONE until and cond are prelude macros; when and dotimes stay special forms
 CLOSED: [2026-09-25]
 =cond= builds its chain through the prelude function =cond-chain= and refuses

lib/macro.ml

@@ -601,10 +601,10 @@ let loaded_for (forms : Form.t list) : loaded option =
       List.filter (fun (n, _) -> Hashtbl.mem taken n) mine
     in
     let all = prelude @ List.map fst mine in
-    (* The common case by a wide margin, and the reason a build that uses no
-       macro pays nothing: a file that calls none costs one scan and no
-       compiler. Without it every build in the suite would link a macro module
-       for the prelude's macros and pay a clang driver to answer nothing. *)
+    (* A file that calls no macro costs one scan and no module. Few do, since
+       cond is a macro; for a file with no macros of its own the module is the
+       prelude's alone, one cached .so shared by every such file, so the usual
+       cost is a stat and a dlopen. *)
     if all = [] || not (List.exists (names_macro all) forms) then None
     else begin
       let extra = rounds ~prelude mine in

test/programs/match-enum.flan

@@ -25,7 +25,15 @@
   (calls)
   :west)
 
+;; recur from inside an arm: the arm is the loop's tail.
+(defn steps-to-west [from Dir] i32
+  (loop [d from  n 0]
+    (match d
+      :west n
+      _     (recur (turn d) (+ n 1)))))
+
 (defn main [] i32
+  (print (steps-to-west :north)) (println "")
   (println (name :north))
   (println (name (turn :north)))
   (println (name (turn (turn :north))))

test/test_acceptance.ml

@@ -423,7 +423,7 @@ let () =
     (* match over an enum lowers to a chain of [=] over one temporary, so
        "(called) " printed once is the scrutinee evaluated once. *)
     let match_enum_out =
-      "north\nsideways\nsouth\n(called) sideways\nback to north\n"
+      "3\nnorth\nsideways\nsouth\n(called) sideways\nback to north\n"
     in
     outputs "match over an enum" "programs/match-enum.flan" match_enum_out;
     outputs ~opt:"-O0" "match over an enum, -O0" "programs/match-enum.flan"