Jack.Tree

data Tree a

A rose tree which represents a random generated outcome, and all the ways in which it can be made smaller.

This tree is exactly the same as 'Data.Tree' in every way except that Applicative '<*>' and Monad '>>=' walk the tree in the reverse order. This modification is critical for shrinking to reach a minimal counterexample.

Constructors

• Node a (List (Tree a))

Instances

• (Show a) => Show (Tree a)
• Functor Tree
• Foldable Tree
• Traversable Tree
• Applicative Tree
• Apply Tree
• Bind Tree
• Monad Tree
• Extend Tree
• Comonad Tree

outcome :: forall a. Tree a -> a

The generated outcome.

shrinks :: forall a. Tree a -> List (Tree a)

All the possible shrinks of this outcome. This should be ordered smallest to largest as if property still fails with the first shrink in the list then we will commit to that path and none of the others will be tried (i.e. there is no backtracking).

foldTree :: forall x b a. (a -> x -> b) -> (List b -> x) -> Tree a -> b

Fold over a 'Tree'.

foldForest :: forall x b a. (a -> x -> b) -> (List b -> x) -> List (Tree a) -> x

Fold over a list of trees.

unfoldTree :: forall b a. (b -> a) -> (b -> List b) -> b -> Tree a

Build a 'Tree' from an unfolding function and a seed value.

unfoldForest :: forall b a. (b -> a) -> (b -> List b) -> b -> List (Tree a)

Build a list of trees from an unfolding function and a seed value.

expandTree :: forall a. (a -> List a) -> Tree a -> Tree a

Apply an additional unfolding function to an existing tree.

The root outcome remains intact, only the shrinks are affected, this applies recursively, so shrinks can only ever be added using this function.

If you want to replace the shrinks altogether, try:

unfoldTree f (outcome oldTree)

filterTree :: forall a. (a -> Boolean) -> Tree a -> Tree a

Recursively discard any shrinks whose outcome does not pass the predicate. /Note that the root outcome can never be discarded./

filterForest :: forall a. (a -> Boolean) -> List (Tree a) -> List (Tree a)

Recursively discard any trees whose outcome does not pass the predicate.