Can't get sound using Racket RSound - racket

Question

I'm trying to play sounds using Racket Rsound. I have a simple program in play.rkt that I'm running with racket play.rkt.
Using play-sound from the GUI library plays the sound as I'd expect:
#lang racket/base
(require racket/gui/base)
(play-sound "/media/tamayo/ExtraDrive1/Dropbox/fclooper/poc/sample.wav" #t)
Output:
$ racket play.rkt
ALSA lib pcm_dsnoop.c:618:(snd_pcm_dsnoop_open) unable to open slave
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
#t ;; plays audio correctly
But using RSound doesn't play any audio:
#lang racket/base
(require rsound)
(play (rs-read "/media/tamayo/ExtraDrive1/Dropbox/fclooper/poc/sample.wav"))
The output is the same as above except for the last line, which is "played sound" instead of #t.
Calling andplay instead also fails:
#lang racket/base
(require rsound)
(andplay (rs-read "/media/tamayo/ExtraDrive1/Dropbox/fclooper/poc/sample.wav" #t))
It also correctly plays audio when I run the same code directly from the Racket REPL:
$ racket
Welcome to Racket v7.3.
> (require rsound)
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching channel map
ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching channel map
ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching channel map
ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching channel map
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock
> (play (rs-read "/media/tamayo/ExtraDrive1/Dropbox/fclooper/poc/sample.wav"))
"played sound" ;; <-- and it does.
>
So the REPL knows how to correctly play audio via RSound, and racket can play using (play-sound ...), but my program just fails. Why?
Details
Ubuntu 18.04
$ racket --version
Welcome to Racket v7.3.
$ uname -a
Linux toast 5.0.0-23-generic #24~18.04.1-Ubuntu SMP Mon Jul 29 16:12:28 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Answer 1

It turns out the program was simply exiting before it got a chance to actually play the sound!
I suppose this should have tipped me off to the fact that RSound works asynchronously:
Plays concurrently with an already-playing sound
This also explains why the REPL worked but the CLI didn't, since the REPL waits around for user input while continuing to run code in the background.
For now, a simple sleep hack works:
#lang racket/base
(play (rs-read "/media/tamayo/ExtraDrive1/Dropbox/fclooper/poc/sample.wav"))
(sleep 10)
(This is part of a looper program which runs forever waiting for user input to do things like swap out the sample sound. That's obviously way out of scope for this question, so sleep is the workaround for now, but in the actual GUI version will become irrelvant.)

Answer 2

According to the documentation for play, the function can't be used in the sub module main.
You can use the function like:
#lang racket/base
(play (rs-read "/media/tamayo/ExtraDrive1/Dropbox/fclooper/poc/sample.wav"))