flan/web/examples/places.flan
Joseph Ferano 26c53e0a19 Every defn in the tree states its return type, and Unit is written ()
The mechanical half, ahead of the parser change that needs it. tools/unit-return.py
fills the empty slot with () and rewrites Unit as () wherever a type is spelled --
(Fn [i32] Unit), (Map i32 Unit), a return type written out.

Deciding whether a defn already had a return type is the whole difficulty, and
the script does it the way parse.ml did: is_type_form is transcribed rather than
improved, because being identical to the parser it replaces is what makes the
sweep meaning-preserving. It is re-runnable, so the lanes that branched before
this can have the same pass at merge:

    python3 tools/unit-return.py .
    python3 tools/unit-return.py --in-strings test/test_flan.ml test/test_acceptance.ml \
        test/test_session.ml emacs/test-flan-dev.el emacs/test-flan-mode.el
    python3 tools/unit-return.py --raw-ml lib/prelude.ml
    python3 tools/unit-return.py --in-html web/index.html

-v logs every defn it saw and what it decided, which is how a sweep of 440 sites
gets reviewed at all. Embedded modes pool a file's type declarations across all
its fragments, because a snippet split across concatenation -- decls ^ "(defn f
[s [u8]] Cursor ...)" -- cannot see the names the other half declared; pooled
names count only in bare-symbol position, for the same reason the prelude's do.
A fragment that cuts off mid-form is skipped rather than guessed at. Five sites
in test_flan.ml still needed a hand, and they are in this commit.

Two things ride along because the sweep needs them: parse.ml reads a lone () as
the return type of a function with no body, which was not a shape the old
optional slot could produce; and the map refusals name () rather than Unit, since
that is now the spelling a caller wrote.
2026-09-12 23:06:40 +07:00

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(defstruct Enemy [hp i32 name string])
(defvar spawned i32)
(defconst room-size 4)
(defvar room [room-size i32])
;; `set` takes a fixed list of forms, not an extensible setf.
(defn main [] ()
(let [e (Enemy {.hp 10 .name "slime"})
p (addr e)]
(set spawned (+ spawned 1)) ; a local or a defvar
(set (.hp e) 7) ; a struct field
(set (.hp p) 8) ; through a (Ptr Enemy) — derefs one level
(set (at room 2) 5) ; a fixed array or slice element
(set (deref p) (Enemy {.hp 3 .name "wisp"})) ; a whole-object store
(print (.hp e)) (println "")
(println (.name e))
(print (at room 2)) (println "")
(print spawned) (println "")))