[ADP-2565] Make runSqlM atomic

[HeinrichApfelmus]

This pull request changes the semantics of runSqlM to become

• atomic in the presence of exceptions
• atomic in the presence of concurrency

This makes the SqlM monad less error-prone and more convenient to use, but disallows some performance techniques, such as SQL savepoints or concurrent access to the SQLite database. However, we need to wrap the monad in a less error-prone interface anyway, and we can always attempt to reintroduce these techniques later, so the gain in convenience is worth the trade now.

This pull request also exposes the exception effect in the SqlM monad explicitly by exposing standard functions such as throw and catch.

Comments

• I have skipped extensive property testing for now, as I want to stabilize the API first. The module Demo.Database provides a basic functionality check.

Issue Number

ADP-2565

[Anviking]

👌

[Anviking]

Did you consider writing these demos as simple unit tests from the beginning?

I imagine it would be little additional work to e.g. replace printTablePerson conn with

selectTablePerson conn
    `shouldReturn`
    [ ("Babbage",1791)
    , ("William",1805)
    , ("Ada",1815)
    ]

[HeinrichApfelmus]

Did you consider writing these demos as simple unit tests from the beginning?

Since I didn't know what the interface will look like, it didn't make sense for me to write the demo as a unit test in the beginning. But I agree that it makes much more sense now, and that's what I intend to do — in a future pull request. 😅