> For the complete documentation index, see [llms.txt](https://romanandreg.gitbook.io/teardown/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://romanandreg.gitbook.io/teardown/theory/purpose.md).

# Purpose

The *correct* teardown of a system becomes a crucial matter when running applications through GHCi while doing REPL driven development; this library provides a stable API to manage the cleanup process of resources your application allocates when it runs for the first time.

This library will:

* Make execution of cleanup `IO ()` sub-routines (e.g. [`Database.PostgreSQL.Simple.close`](https://hackage.haskell.org/package/postgresql-simple-0.5.3.0/docs/Database-PostgreSQL-Simple.html#v:close)) idempotent. This helps avoiding runtime exception of the "already closed resource" nature.
* When composing with other cleanup `IO ()` sub-routines, one can use the `(>>)` operator, but what happens if the sub-routine throws an exception? Likely other resource cleanup sub-routine is not going to be executed because of a runtime exception. This library allows the composition of multiple cleanup `IO ()` sub-routines, while also ensuring that despite failures every resource cleanup is executed.
* All teardown sub-routines use a description argument to keep track of what is being cleaned up; By requiring this description, we avoid confusion around what is going on when shutting down an application. This library makes this documentation a /required/ argument when building teardown sub-routines, thus helping trace-ability.
* Keeps track how much time every teardown sub-routine takes, allowing the developer to learn which parts of the teardown procedure are slow and adequately address those on development time (e.g., Faster reload => Faster development feedback loops).

By using this library, you may implement without much effort a good, reliable and transparent strategy for application resource teardown sub-routines.