The Windows program "wsl.exe" is the interop program that ties things
together. You can call it and pass it a command to be executed within
the WSL environment.
So, while I can simply say "lilypond" in a WSL shell, under a Windows
shell I need to say "wsl lilypond" to have the same effect. Note then
that I am technically running "wsl.exe", not "lilypond"; but "lilypond"
will end up a child process of "wsl.exe" with standard input/output
properly routed.
Interesting...
...so cd'd into a directory with simpl LP files and there issued
wsl -e lilypond -- voice-choir-satb.ly
and it worked!
[upon reading further I realize, you already wrote that]
Note:
I already had the linux version of LP installed on my maschine and sometimes
use it from within a WSL bash shell.
[stuff on paths and mount points snipped]
…which is rather wordy, but would get the job done. For Frescobaldi,
however, we'd would likely need an intermediate script that translates
file paths. But this is probably non-trivial, as there are a few cases
where paths could show up and need conversion (e.g.
"-dinclude-settings=" would need to be handled).
I think that should not be a problem since Frescobaldi composes the cmdline
anyway and does know all the bits and pieces. After all on windows Frescobaldi
invokes the windows version of lily in a separate process already.