flan/conditions-play.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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;;;; A program to poke at conditions and restarts with — see conditions.org.
;;;;
;;;; It loops instead of exiting, so `flan dev conditions-play.flan` can attach
;;;; and you can redefine `probe` and `run-once` from Emacs while it runs. The
;;;; socket written here is only a fallback; the daemon overrides it.
(import agent "vendor:agent")
(defstruct AssetMissing [id i32])
(defstruct Corrupt [id i32])
;;; Handlers cannot see the establishing function's locals yet, so anything a
;;; handler accumulates into has to be a global.
(defvar seen i64)
(defvar ticks i64)
;;; Two frames under the restart-case, so a transfer has something to cross.
(defn probe [n i32] i32
(signal (AssetMissing {.id n}))
100)
(defn middle [n i32] i32
(defer (set ticks (+ ticks 1))) ; runs on the way out, transfer or not
(+ (probe n) 1))
;;; The shape spec-conditions.md §1 uses: a restart-case in value position,
;;; whose fall-through has to produce the type too.
(defn fetch [n i32] i32
(restart-case (middle n)
(use-placeholder [] -1)
(retry [] 7)))
(defn run-once [] ()
(print (fetch 1)) (println "")
(handler-bind [(AssetMissing [c] (set seen (+ seen (i64 (.id c)))))]
(print (fetch 2)) (println ""))
(handler-bind [(AssetMissing [c] (invoke-restart 'use-placeholder))]
(print (fetch 3)) (println ""))
(print seen) (println "")
(print ticks) (println ""))
(defn main [] i32
(agent/start "/tmp/flan-conditions.sock")
(run-once)
(while (= (agent/wait 200) 0) 0)
(run-once)
(while (= (agent/wait 200) 0) 0)
(run-once)
0)