The daemon owns the program's lifetime, so the terminal it was started in
was also the only place that program could be stopped from. M-x flan-dev
builds, launches and connects; M-x flan-dev-quit ends it.
It waits for a connection rather than for the socket file to appear: the
daemon unlinks a stale socket before binding, so waiting on the file either
succeeds instantly against nothing or races the unlink. And when the daemon
dies before binding — which for a program that does not compile is the
ordinary failure — the refusal names its buffer, because that is where the
compiler's reason is and nothing this end sees says it.
Its stdout is a pipe into the daemon now, and whatever it printed since the
last reply rides along with the next one into *flan-output*. Arriving with a
reply rather than by a separate request is the point: the output an evaluation
itself caused is the output anyone wants to see.
Draining that pipe is a liveness requirement, not a nicety. A pipe nobody reads
fills at 64K and the next write blocks the program forever, so it is read from
the accept loop's select whether or not an editor is asking, and the buffer is
capped - a program printing every frame must not grow the daemon without limit,
and the newest text is the useful end.
test_dev read the program's transcript off the daemon's stdout, which is no
longer where it goes; it collects :output from replies instead, which is also
what the editor does. The emacs test moved to a fixture that keeps running,
since it now evaluates more times than the old one had reloads to give.
C-c C-c recompiles the top-level form at point and installs it in a running
program at that program's next frame boundary. Verified against sand: an
unsaved buffer edit to game-draw, and 240 consecutive frames drew it.
flan-mode.el derives from prog-mode with lisp-mode's syntax table, which is
most of the work - Flan is s-expressions, so sexp motion, paren matching,
beginning-of-defun and indentation are already right. What it adds is Flan's
own brackets ([ and { are brackets and not symbol characters, since every
binding list and every type is written with them), the characters a name may
contain, and its keywords.
flan-dev.el has no parser in it, which is what the protocol choice bought:
prin1 writes a request, read reads a reply. C-c C-k sends a buffer as one
module rather than a form at a time, because a defvar and the function using it
have to arrive in the same load or the first refers to storage that does not
exist yet. An error comes back with a location and point moves there.
Framing is in bytes and Emacs counts characters, so every length goes through
string-bytes and the process is binary. Otherwise one non-ASCII character in a
buffer puts the reply stream out of step by exactly as many bytes as the
payload has of them - a bug that reads as a corrupt protocol and only appears
for some people. test_emacs.ml drives the real client against a real daemon for
that reason: it is not the same claim as the daemon answering correctly, and a
mistake in the framing, in beginning-of-defun over Flan's syntax table, or in
the reply reader passes test_dev.ml and fails here.
