flan/examples/text-writing-anim.flan
Joseph Ferano 2e203f64b8 bytes copies, bytes-view aliases, and a dev-session segfault parks
The INSERTIONSORT crash, all three rulings (FIX.org 2026-09-20):

- (bytes s) allocates a writable copy through the allocator surface —
  context or (bytes s a), StorageExhausted with retry, a registry note in
  dev builds (flan_bytes_dup, lowered like vec-new). (bytes-view s) is the
  old zero-cost reinterpret, renamed, read-only by convention; every
  in-repo reader swept over to it. (string b) unchanged.
- String constants were already read-only on both backends at -O0; now
  pinned — bytes-copy.flan rows on LLVM/-O0/--x86, and dies_segv rows
  asserting the write-through-view trap on both backends.
- A dev build installs a SIGSEGV/SIGBUS handler by the same dev-only
  constructor slot that arms the registry: one line naming the address and
  the innermost frame, then the trap-hook park — stopped, not dead, the
  daemon serving. No agent: message and re-raise. Release builds untouched.
  Pinned by trap_park over dev-segv.flan.
2026-09-20 23:12:42 +07:00

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;;;; raylib [text] example - text writing anim
;;;;
;;;; examples/text/text_writing_anim.c. Sixty lines of C whose whole substance
;;;; is one call this package cannot bind:
;;;;
;;;; DrawText(TextSubtext(message, 0, framesCounter/10), ...)
;;;;
;;;; TextSubtext is in raylib.h and is not in the bindings, on the rule
;;;; raylib.flan states for the whole Text* family: it answers a `char *` into
;;;; a rotating static buffer, and declare-c refuses a returned pointer to
;;;; memory the caller does not own. There is no missing line to add — the
;;;; binding would be wrong at any signature.
;;;;
;;;; And it does not matter, because Flan has the operation as a primitive.
;;;; `(slice a lo hi)` takes a view of an array, `(string b)` reinterprets the
;;;; bytes as a string at no cost, and `(string (slice message 0 n))` is
;;;; TextSubtext with the static buffer removed — no copy, no shared state, no
;;;; rotation to run out of. Porting the example is therefore how the gap gets
;;;; *closed* rather than reported: the C's workaround for not having slices
;;;; is the thing Flan did not need.
;;;;
;;;; The one place they differ, and it is why the clamp below is here rather
;;;; than in the C: TextSubtext clips its length to the string, so the C can
;;;; pass a counter that runs past the end for ever and see nothing happen.
;;;; `slice` does not clip — an out-of-range bound is an error, and a bound
;;;; computed at run time is checked at run time — so the length has to be
;;;; brought inside the string before the call. That is a better failure than
;;;; the C's, and it costs one `min`.
;;;;
;;;; The message is a `[u8]` and not a `string` because `slice` takes an array
;;;; or a slice; `(bytes-view "…")` is the bridge in the other direction from
;;;; `(string …)` and costs nothing either. The embedded newline is written as
;;;; an escape, and raylib's draw-text breaks the line on it.
(import rl "vendor:raylib")
(defconst screen-width 800)
(defconst screen-height 450)
(defconst message
"This sample illustrates a text writing\nanimation effect! Check it out! ;)")
(defvar frames-counter i32)
(defn main [] ()
(rl/init-window screen-width screen-height
"raylib [text] example - text writing anim")
(defer (rl/close-window))
(set frames-counter 0)
(rl/set-target-fps 60)
(until (rl/window-should-close?)
;; Update. Holding space runs the counter eight times faster; enter starts
;; it over.
(if (rl/key-down? :key-space)
(set frames-counter (+ frames-counter 8))
(set frames-counter (+ frames-counter 1)))
(when (rl/key-pressed? :key-enter) (set frames-counter 0))
;; Draw
(rl/with-drawing
(rl/clear-background rl/raywhite)
;; One character every ten frames. The clamp is the whole difference from
;; the C — see the header comment.
(let [b (bytes-view message)
n (min (i32 (len b)) (/ frames-counter 10))]
(rl/draw-text (string (slice b 0 n)) 210 160 20 rl/maroon))
(rl/draw-text "PRESS [ENTER] to RESTART!" 240 260 20 rl/lightgray)
(rl/draw-text "HOLD [SPACE] to SPEED UP!" 239 300 20 rl/lightgray))))