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Posted on 2023-01-21
Recently I was learning a little bit of Lisp for something I may reveal in a few months. But a few days ago I hit a major roadblock, Lisp is running programs weirdly.
To my knowledge, the following runs programs with an input and gets its output as a string:
(setq output-string
(with-output-to-string (stream)
(uiop:run-program
'("rev")
:output stream
:input '("Hello World")
)
)
)
This is working fine (tested with the sbcl-compiler).
It can also run curses programs fine with interactive stdin and stdout:
(uiop:run-program
'("vim")
:output :interactive
:input :interactive
)
The problem is combining both, piping input into stdin, interacting with the program and getting the output from stdout. There are some programs that require this, e.g. fzf takes a list of newline-separater strings and lets the user choose from these to return to the output. The dynamics of how programs can do this is a little bit complicated, but basically it requires reading the entire input, re-opening the input from the TTY, opening the TTY as the output, running curses (or any similar library), resetting the output and finally returning the result. How I would run such programs in Lisp is the following:
(setq output-string
(with-output-to-string (stream)
(uiop:run-program
'("fzf")
:output stream
:input '("Hello World Hello")
)
)
)
But this does not work and blocks the entire application. Replacing fzf with a little program written by myself shows that the call to curses initscr blocks. Maybe, I thought, I actually did something that was not possible in any programming language, so I re-implemented it in Rust, and it works fine. Here is the equivalent Rust code:
let mut out = Command::new("fzf")
.stdout(Stdio::piped())
.stdin(Stdio::piped())
.spawn()?;
let stdin = out.stdin.as_mut().unwrap();
stdin.write_all(b"Hello\nWorld")?;
drop(stdin);
let output = out.wait_with_output()?;
let string = String::from_utf8(output.stdout)?;
Furthermore, it also obviously works in any normal shell, simply with:
echo "Hello\nWorld" | fzf
So something is weird with how Lisp (or uiop) runs programs.
Honestly, I don't know. There is something weird going on I don't understand. Either this is a bug in uiop or I am missing some argument. Maybe there are some Lisp-magicians here to whom this is obvious, but I am stuck. Either I will find a resolution to this issue or will just rewrite this (small) Lisp program in another programming language.