Struct texlang::vm::ShutdownSignal

pub struct ShutdownSignal {}

A signal that the VM is shutting down.

A value of this type is returned in the error payload of the Result of Texlang commands and basically all other Texlang functions. The only thing to do with the signal is to propagate it up the Rust call stack using Rust’s ? operator. Eventually the signal will reach the main VM loop, and the VM will stop.

The stop signal should not be ignored or otherwise “handled”. For example, this code is incorrect:

fn execution_primitive_fn<S: TexlangState>(
   token: token::Token,
   input: &mut vm::ExecutionInput<S>,
) -> txl::Result<()> {
    let i = match i32::parse(input) {
        Ok(i) => i,
        Err(_shutdown_signal) => {
            // This is incorrect - the shutdown signal must be propagated!
            0
        }
    };
    println!["Parsed integer {i}"];
    Ok(())
}

In this case the VM will eventually panic when it realizes that the shutdown was ignored. The correct code is this:

fn execution_primitive_fn<S: TexlangState>(
   token: token::Token,
   input: &mut vm::ExecutionInput<S>,
) -> txl::Result<()> {
    let i = i32::parse(input)?;
    println!["Parsed integer {i}"];
    Ok(())
}

Generating the shutdown signal

The signal can originate either with a fatal error, or from a TeX control sequence that wants to stop execution (e.g. the \end primitive).

Trait Implementations

impl Debug for ShutdownSignal

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.