Improved, and dare I say minimal, shrinking of lists #276
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jacobstanley
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Apr 25, 2019
| @@ -305,9 +363,20 @@ class Monad m => MonadGen m where | |||
| -- | |||
| freezeGen :: m a -> m (a, m a) | |||
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| instance Monad m => MonadGen (GenT m) where | |||
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We remove the MonadGen instance for GenT, so the combinators in Hedgehog.Gen will now only work on Gen or transformers including Gen as the base monad.
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In the 99% case, users will just use Gen by virtue of the type of forAll and not worry about any of this.
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Updated description with details |
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Good stuff 馃榿 |
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Crazy stuff 馃殌 |
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This PR provides significantly improved shrinking of lists, I believe Hedgehog should now offer virtually minimal shrinking in this area. The change is that now the list shrink tree can alternate between shrinking the list and shrinking the elements. Before it would shrink all the elements first, and then it would try to shrink the list.
We also simplify
MonadGensignificantly, with all functions being implemented in terms oftoGen/fromGen. This comes at the cost ofStateTandRWSTinstances, but you can still run these on the inside of the transformer and get aMonadGen, it's just slightly less conveniant. If anyone can figure out how to implementMonadTransControlforTreeTthen they will be easy possible on the back of that.Many thanks to @edsko 馃挴 for the detailed discussions about the improvements offered here, and for his implementation of
interleavefor trees with monadic effects, that is a nut I've been trying to crack for many years now. It is quite a relief to have it solved! 馃帀