Macro condition 

macro_rules! condition {
    (class = $class:expr, data = $data:tt, $($arg:tt)*) => { ... };
    (data = $data:tt, $($arg:tt)*) => { ... };
    (class = $class:expr, $($arg:tt)*) => { ... };
    ($($arg:tt)*) => { ... };
}

Signal a generic R condition from Rust with rust_condition class layering.

Rides the tagged-condition transport that every #[miniextendr] function uses. Unlike error!, a bare condition is a silent no-op if there is no handler. The raised condition has class c("rust_condition", "simpleCondition", "condition").

An optional class = "name" form prepends a custom class. An optional data = ... form (after class, before the message) attaches named fields readable as c$<name> in handlers — same grammar and supported value types as crate::error! (see there for details).

See also

• crate::error! / crate::warning! / crate::message! — louder condition kinds. Pick condition! when “no handler = silent” is the right default (progress events, structured logging hooks).
• std::panic! — escape hatch when the failure cannot be ignored.
• crate::error_value — tagged-SEXP transport rationale.

Name-collision note. Because pub mod condition exists at the crate root, use miniextendr_api::condition imports the module rather than this macro. Invoke via miniextendr_api::condition!(...) (fully qualified) or via mx::condition!(...) after use miniextendr_api as mx;.

Example

use miniextendr_api::condition;

#[miniextendr]
fn signal_progress(n: i32) {
    condition!(class = "my_progress", "processed {n} items");
}

withCallingHandlers(
  signal_progress(42L),
  my_progress = function(c) cat("progress:", conditionMessage(c), "\n")
)
# progress: processed 42 items