# Tracking records that could not be processed

## The `NotCompleted` object

This is an object returned when a composable function did not complete a task. `NotCompleted` is a special result type that can be produced by a composable app. These objects evaluate to `False`.

An app can return a `NotCompleted` result for one of 2 reasons. The object contains information regarding the input data, where the issue arose and whatever message was provided by the code (like an exception traceback).

## `NotCompleted` FALSE type

The results when a condition was not met. For example, below I create an app that will return alignments that with 2 specific sequences but I’m including one that does not exist (“Mouse”). So this will fail.

## `NotCompleted` ERROR type

An `ERROR` type is returned if an exception is raised during the calculation. We trigger it in this case by trying to open a non-existent file.

## Composed functions propagate `NotCompleted` results

and