restart-case

(restart-case form (restart-name (arg...) [:report r] [:interactive i] [:test t] body...)...)

Evaluates form with one restart established per clause for its dynamic extent. Nothing happens on normal completion — the form's values are returned and the restarts are disestablished. When code running inside the form (typically a handler-bind handler, running at the signal point) invokes one of the restarts with invoke-restart, control unwinds back to the restart-case (running intervening unwind-protect cleanups) and the clause body runs in the restart-case's own lexical environment with the invocation arguments bound to arg... — so a clause body can return-from an enclosing function or go to a tag of an enclosing tagbody (the retry-loop idiom). The restart name may be a symbol or a keyword; find-restart returns the innermost active restart as a first-class object and compute-restarts lists them all. The :report, :interactive and :test options are accepted and stored in the restart record (nothing in rontolisp renders reports or invokes restarts interactively — there is no debugger).

Supported on every backend except --no-gc, which keeps the historical lowering to the primary form. A restart-system program compiles in EH mode on the wasm-GC backends. Lite deviations: &optional clause parameters take nil instead of their default when not supplied, restarts are not associated with conditions (the optional condition argument of find-restart is ignored), and a restart object prints as a plain list rather than #<RESTART ...>.

A handler invokes the restart by keyword name, with arguments; the clause body's value becomes the value of the whole form:

The retry idiom — a clause body going back into an enclosing tagbody: