resumable evaluates an expression in a context that can intercept named resumptions.

Syntax

(resumable ⟨expr⟩
  ((⟨resumption-ctor⟩ ⟨pattern⟩ ...) ⟨handler-body⟩ ...))

Semantics

  • The first subform is the expression that may invoke resume-to.
  • Each branch must match a resumption constructor, not an arbitrary pattern.
  • Patterns on constructor fields are tried in order. If no branch matches the value, it is offered to an enclosing handler for the same resumption. A resumption with no matching handler signals an error.
  • When a matching resumption is signaled, control transfers to the handler body.
  • The result type of each handler must agree with the result type of the whole resumable expression.

Example

(define (make-breakfast-with egg)
  (resumable (Some (cook (crack egg)))
    ((SkipEgg) None)
    ((ServeRaw _) (Some egg))))