[Haskell-cafe] ANN: Important lambabot update (5.0.2.1 release)

[Bertram Felgenhauer]

Hi,

> Generally, lambdabot relies on SafeHaskell and not running user-supplied
> IO actions for safety. This is unlikely to be bullet-proof, so it's
> advisable to sandbox mueval. However, the @check command violated this
> basic principle, and allowed running arbitrary IO actions.

This was deliberately vague. The point is that @check took an arbitrary
value of type Property, and ran it. That type is based on IO, and there
are actually direct ways of incorporating an IO action into a Property:

 * ioProperty (alias morallyDubiousIOProperty)
 * whenFail, whenFail'

In the end, rather than trying to control whether these functions are
imported (which would be a fool's errand, because Test.QuickCheck is a
Safe module, and can be reexported from other modules), I came up with
the QuickCheck-safe design whose SProperty type does not embed IO
anywhere.

Cheers,

Bertram