Failure

Inspecting detached failures.

Fail.attemptReport and Fail.attemptDiagnostic report cleanup failures raised while a computation unwound as Failure snapshots. A snapshot names the effect operation that failed and keeps its arguments, but exposes no handler or resumption. Snapshots retain their payloads, including resources; keeping a snapshot does not extend a resource’s lifetime.

Failure

type FailureSource

A detached snapshot of one failure: the aborting operation and its arguments, with any failures suppressed beneath it. Show renders a metadata summary containing the effect, operation, argument count, optional trace, and nested suppressed failures. Argument contents remain opaque: snapshots do not retain their Show dictionaries.

Instances:

Show Failure

argument

argument : Int -> Failure -> Maybe aSource

The argument at a zero-based index, when it has the requested type, including all its type arguments. A wrong type, an index out of range, and a type containing functions or resources answer Nothing. An ordinary immutable type is inspectable without exposing its constructors: annotating payload : Maybe IO.Error and binding payload = Failure.argument 0 failure reads an IO error.

argumentCount

argumentCount : Failure -> IntSource

How many arguments the failing operation was given.

effectName

effectName : Failure -> StringSource

The name of the effect whose operation failed, such as Fail.Fail.

operationName

operationName : Failure -> StringSource

The name of the operation that failed, such as Fail.fail.

suppressed

suppressed : Failure -> List FailureSource

The failures suppressed beneath this one, which keep their own.

trace

trace : Failure -> Maybe (List Frame)Source

The stack captured at this failure’s original abort site, innermost first. Nothing means its handler did not request capture; Just [] means capture was requested but found no frames. Reading a snapshot never captures the current stack. Nested suppressed failures keep their own optional traces.