What is a shrink, with regard to Haskell's QuickCheck?

Question

I\'m learning the ropes of QuickCheck >= 2.6 but I don\'t understand what a shrink is. From looking at the type signature shrink looks more like expand! Please illuminate me :)<

Answer 1

A single shrink is a stepwise reduction in complexity of some Arbitrary test case (an "immediate shrink"). This might be something like 2 -> 1 or 1:[] -> []. For more complex types there may be multiple ways to "incrementally shrink" a type so you specify all of them in a list.

For example, trees might be shrunk by removing any one leaf, thus if there are n leaves then shrink produces a list of length n.