Stream: show and tell

Topic: thoughts on roc for scripting

removewingman (Oct 22 2026 at 23:30):

roc for scripting

I experimented with roc for scripting and want to share my thoughts and experience.

I replaced a 10 line posix shell script and a more complex janet script with roc.

original posix script:

#!/bin/sh

tmpTYPSTFile="/tmp/typst2pdf$$.typ"
tmpPDFFile="/tmp/typst2pdf$$.pdf"
trap 'rm -f -- "$tmpTYPSTFile" "$tmpPDFFile"' EXIT TERM INT QUIT

 [ -t 0 ] && { printf "%s: stdin not provided\n" "$0" >&2 ; exit 1; }

cat > "$tmpTYPSTFile"

typst compile --pdf-standard 2.0 --format=pdf "$tmpTYPSTFile" "$tmpPDFFile"

cat "$tmpPDFFile"

same script in roc

#!/usr/bin/env roc

app [main!] {
    pf: platform "https://codeberg.org/removewingman/restricted-roc/releases/download/v0.2.0/DP5N5ev2nXZ1XSKWHPQZnjSLz5CmfCxYm3QAfrrMxoWR.tar.zst",
}

import pf.Stdin
import pf.Stdout
import pf.Stderr
import pf.Script
import pf.File
import pf.Process

main! = |args| {
    Script.stdin_provided_else_exit!({ message: "${args.get(0)?}: stdin not provided" })?
    input_file = File.create_bytes_tmp!({ name: "typst2pdf", extension: "typ", bytes_content: Stdin.bytes!()? })?
    output_file = File.tmp_name!({ name: "typst2pdf", extension: "pdf" })?
    match Process.run!({ bin: "typst", args: "compile --pdf-standard 2.0 --format=pdf ${input_file} ${output_file}" })?.success_and_stderr_empty({ error_message: "typst error" }) {
        Ok(_) => {
            output = File.content_bytes!({ absolute_path: output_file })?
            Stdout.write_bytes!(output)
        }
        Err((result, message)) => {
            result.exit_write_to_stderr!(message)
        }
    }
}

• janet script pr

What I like

• similar to janet
  • both writing a script in one file and expanding into multiple files if it gets to much are possible and can turn into a binary
  • compile time checks, type interference
  • feels simple and smooth
• import exposing
• !, ?, dbg and crash
• string handling and multiline strings
• descriptive error handling and easy of use to introduce new errors
• ability to scope into mutability
• not having Optionals

What I am unsure about / could be better

• implementation of trap functionality
  • platform tracks tmp files and deletes them after program execution, feels right not sure tho
• platform api (I implemented this, but could change lol)
• builtins for the ! and try? functions, e.g. for_each_try!
• importing multiple things like so import pf.[Stdin, Stdout] (anything so 10 lines are not wasted on imports)
• shadowing local variables bindings inside a function scope (I know this has been discussed, just want to state my experience)
  • every popular scripting language (Python/Janet/Lua/Ruby) has this feature, I missed it

• structural records to have defaults

  • tmp_name! : { name: Str, extension: Str, automatically_delete: Bool ?? true } => Try({}, [FileCreateErr(Str)]) (throws compile error)

• roc works on more unix systems e.g. FreeBSD/OpenBSD

• smaller, simpler and more clear error and warning compiler messages when using check

Conclusion

• Would I use roc to replace a 10 line posix script? Probably not.
• Would I use roc to write a bit more complex scripts instead of Janet/Python/Ruby/Lua ? Absolutely.
  • obv. for e.g. a river wm there has to be the ecosystem
• Would I like roc more as a config language instead of Lua/Toml/Janet? Definitely.
  • afaik, it is already one of roc's goals to be as easy embeddable as Janet/Lua

Let me know what you think :)

Anton (Oct 23 2026 at 08:45):

Thanks for sharing your experience @removewingman :)

Anton (Oct 23 2026 at 08:46):

shadowing local variables bindings inside a function scope

Are you aware of the var keyword?

Anton (Oct 23 2026 at 09:01):

structural records to have defaults

We used to have these but it resulted in a lot of problems with type checking, so it was removed.

Anton (Oct 23 2026 at 09:08):

Looks like you made PR#11096 for for_each_try! but you closed it :sweat_smile:

removewingman (Oct 23 2026 at 09:18):

I am aware of the var keyword, meant something like this:

a = "b"
a = a.trim()

Yeah, I know. If I have some better hardware and some local AI Agent will try to contribute to roc Builtins.
Having to test everthing in CI is annoying.

Last updated: Nov 04 2026 at 18:54 UTC