Gist demonstrating the ability to run Crystal code from Rust.

logged.rs

#[link(name = "logger")]
extern {
    fn CrystalLog(text: *const u8);
}

fn log(text: &'static str) {
    unsafe{ CrystalLog(text.as_bytes().as_ptr()) };
}

fn main() {
    log("Hello Crystal, from Rust!");
    log("Logging from Crystal, using Rust, totally works twice, by the way.");
}

logger.cr

require "colorize"

fun log = CrystalLog(text: UInt8*): Void
  # We need to initialize the GC
  GC.init

  # We need to invoke Crystal's "main" function, the one that initializes
  # all constants and runs the top-level code (none in this case, but without
  # constants like STDOUT and others the last line will crash).
  # We pass 0 and null to argc and argv.
  LibCrystalMain.__crystal_main(0, Pointer(Pointer(UInt8)).null)

  #puts "#{"Pointer Recieved:".colorize.bold} #{text}"
  #puts "#{"Value of Pointer:".colorize.bold} #{String.new(text)}"
  puts String.new(text)
end

run.sh

crystal logger.cr --link-flags "-dynamiclib" -o lib/x86_64-apple-darwin/liblogger.dylib
rustc logged.rs
./logged