I created the following arc command script:

[script start]

#! /bin/sh ## arc: launcher for Arc. Put this file in your $PATH and chmod +x it.

ARC_DIR="/home/user/arc3/" # change this, obviously

rlwrap mzscheme -qr ${ARC_DIR}as.scm $@ # $@ holds the list of cmdline args

# notice the mzscheme switch is "-qr" and not "-f" here

[script end]

I then created the following run-hacker-news.arc:

[script start]

#!/usr/bin/env arc

(load "news.arc")

(nsv)

[script end]

I then run this by:

./run-hacker-news.arc

Because I just tried, and something like:

  [script launch-asv.arc]
  #!/usr/bin/env arc
  (asv)
  [script end] 

  $ chmod +x launch-asv.arc && ./launch-asv.arc &
  [1] 2439
  $  # there is no "serving on 8080" message, but...

Anyway yes, Lisp is special, and the use of `screen' or the like may be better.

[cmdline start]

linuxbox arc3 # patch -p1 < ../arc-unix.patch (Stripping trailing CRs from patch.) patching file ac.scm Hunk #1 succeeded at 1112 (offset -15 lines). (Stripping trailing CRs from patch.) patching file as.scm [cmdline end]

The patch did seem to apply but not perfectly.

Now I get:

[cmdline start]

linuxbox arc3 # ./run-hacker-news.arc reference to undefined identifier: empty?

[cmdline end]

which has (asv) in it just like your example script. If I call arc command script I get the same error. This is arc3.1.tar from ycombinator.com

Also what does (asv) do instead of (load "news.arc") (nsv)? I don't know lisp but will surely learn if I can get this running for starters.

Strange, which version of mzscheme do you use (`mzscheme -v')? 'empty? is in the MzScheme base "scheme" module for me (MzScheme 4.2.1)!

Anyway, 'empty? is called only in as.scm, and you can actually leave this file unchanged for your case (I think). Just patch ac.scm.

> Also what does (asv) do instead of (load "news.arc") (nsv)?

'asv is used to start the "Appplication server" defined in "app.arc". App.arc is generic, and news.arc use/require it. I use it in the example to see if maybe it was a problem w/ news.arc specifically (and because I feel lazy about typing "(load ...)": app.arc is in the Arc "stdlib" (see the file "libs.arc"), and so is loaded by default).

'nsv is defined like this, in "news.arc":

   (def nsv ((o port 8080))
     [...]        ; do news-specific init stuff...
     (asv port))  ; relay to 'asv, which itself relays to 'serve (defined in srv.arc)

> How are generally other people running it detached?

They don't: Arc is different :-D

---

Ah also, to start the news server in the background, no need of a script, you could use:

  $ echo '(nsv)' | arc news.arc - &

  in as.scm:

  -      (for-each (lambda (f) (aload f)) args)  ; ...execute them!
  +	 (for-each (lambda (f) (if (string=? f "-") (tl) (aload f))) args)

Once again, consider `screen'. Arc has no Unix signal handling for instance, so an "Arc daemon" would not be "powerful". The only possible interaction would be to kill it (via `kill'). Better keep an eye on it, i.e: keep a REPL opened to manage your forum.

---

I am using mzscheme 372 as described here: http://arclanguage.org/install

I tried:

  $ echo '(nsv)' | arc news.arc - &

  arc> Error: "Bad object in expression #<eof>"
  arc> Error: "Bad object in expression #<eof>"
  ...

http://arclanguage.org/install has not been updated, but the big feature of the 3.1 version is that it can runs on recent (> 4.1) MzScheme. See http://arclanguage.org/item?id=10254.

Edit: oh yes, maybe you use Arc 3! The current version is Arc 3.1: see the previous link. Direct download: http://ycombinator.com/arc/arc3.1.tar. The patch is to be used with the 3.1!

> To be honest, a web service without daemonizing does not sound very intuitive. When I say I need to stay connected to the server to keep the service alive, forums users say "Ah man, what kind of a computer engineer are you?"

I agree it's not intuitive, but the use of `screen' + long-lived REPL to manage the forum can actually be seen as quite smart:

  $ screen arc
  arc> (load "news.arc")
  arc> (thread:nsv)   ; start it in a new thread, to not block the REPL
  arc> ^A d  ; CTRL-A d, to detach the `screen'
  [detached]

At any time, you can login back to the server and do:

  $ screen -r   # resume
  arc> ; you're in front of the forum REPL
  arc> requests*  ; ultra basic analytics: show the number of requests served
  161803
  arc> (change-some-settings)  ; you get the idea

  arc> (exit)  ; or just ^D if you have applied the patch
  [screen is terminating]
  $ 

If you really want to just echo '(nsv)' | arc news.arc -, then use version 3.1, the patch and a small shell or Perl wrapper script to daemonize the Arc process. Some fork + redirect standard ports + setsid magic, then exec the Arc process.

In Perl, from `perldoc perlipc':

      use POSIX 'setsid';

      sub daemonize {
          # chdir '/'               or die "Can't chdir to /: $!";
          open STDIN, '/dev/null' or die "Can't read /dev/null: $!";
          open STDOUT, '>/dev/null'
                                  or die "Can't write to /dev/null: $!";
          defined(my $pid = fork) or die "Can't fork: $!";
          exit if $pid;
          setsid                  or die "Can't start a new session: $!";
          open STDERR, '>&STDOUT' or die "Can't dup stdout: $!";
      }

  (load "news.arc")
  (nsv)

Here's what I normally do as per how-to-run-news.txt

mzscheme -f as.scm

I get the mzscheme prompt. I type:

(load "news.arc") (nsv)

It runs well, so far so good, but I have the interactive interpreter. As soon as I shut down, the service disappears.

To run it as a shell script I looked at mzcheme man page and tried to run the following in a script called run_hacker_news.sh:

[script starts] #! /bin/sh #|

exec /home/bahadir/mz/bin/mzscheme -f as.scm |# (load "news.arc") (nsv) [script ends]

  Or indent a line by at least two spaces to get text verbatim.