12 Guard
| (require koyo/guard) | package: koyo-lib |
This module provides utilities for implementing early returns from request handlers and other procedures.
Within a with-guard form, ends execution early if
expr is #f. If expr is not #f, it
is returned normally. On early exit, when the first form is used, the
result of the with-guard form is the application of form’s
guard procedure. When the second form is used, the result of the
with-guard form is else-expr. Use outside the body
of a with-guard form is a syntax error.
Added in version 0.28 of package koyo-lib.
syntax
(with-guard guard-proc-expr body ...+)
Captures an escape continuation that is used to abort the
execution of bodys when a guard condition fails. The
guard-proc-expr is a procedure that is executed when a
guard without an #:else keyword fails.
Examples:
> (require koyo/guard)
> (with-guard (lambda () 'not-found) (guard #f) (displayln "unreachable")) 'not-found
>
> (with-guard (lambda () 'not-found) (guard #t) (guard #f #:else 42) (displayln "unreachable")) 42
Added in version 0.28 of package koyo-lib.