Add shrinkBoundedEnum function.
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The `shrinkBoundedEnum` function provides a counterpart to the
pre-existing `arbitraryBoundedEnum` function.
Together, they can be used to define a complete `Arbitrary` instance for
a bounded enumeration data type.
For example, let's say we have the following type:
```hs
data MyEnum
= E00 | E01 | E02 | E03 | E04 | E05 | E06 | E07 | E08 | E09
| E10 | E11 | E12 | E13 | E14 | E15 | E16 | E17 | E18 | E19
| E20 | E21 | E22 | E23 | E24 | E25 | E26 | E27 | E28 | E29
| E30 | E31 | E32 | E33 | E34 | E35 | E36 | E37 | E38 | E39
| E40 | E41 | E42 | E43 | E44 | E45 | E46 | E47 | E48 | E49
| E50 | E51 | E52 | E53 | E54 | E55 | E56 | E57 | E58 | E59
| E60 | E61 | E62 | E63 | E64 | E65 | E66 | E67 | E68 | E69
| E70 | E71 | E72 | E73 | E74 | E75 | E76 | E77 | E78 | E79
| E80 | E81 | E82 | E83 | E84 | E85 | E86 | E87 | E88 | E89
| E90 | E91 | E92 | E93 | E94 | E95 | E96 | E97 | E98 | E99
deriving (Bounded, Enum, Eq, Ord, Show)
```
We can then define the following arbitrary instance:
```
instance Arbitrary MyEnum where
arbitrary = arbitraryBoundedEnum
shrink = shrinkBoundedEnum
```
Since `shrinkBoundedEnum` reuses `shrinkIntegral` internally, we get similar
shrinking behaviour.
Values earlier in the shrink list are shrunk more aggressively, followed
by exponential back-off:
```hs
>>> shrinkBoundedEnum E99
[E00,E50,E75,E87,E93,E96,E98]
```
```hs
>>> shrinkBoundedEnum E49
[E00,E25,E37,E43,E46,E48]
```
```hs
>>> shrinkBoundedEnum E01
[E00]
```
```hs
>>> shrinkBoundedEnum E00
[]
```
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Hi @nick8325 Just wondering if you think this function would be useful? If you like the idea, but you'd like me to make revisions to it -- let me know, would be happy to do so. All the best! |
|
It looks good! Thanks for the patch! |
You're welcome! |
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This PR adds a new function
shrinkBoundedEnum, which should resolve issue #343.The
shrinkBoundedEnumfunction provides a counterpart to the pre-existingarbitraryBoundedEnumfunction. Together, they can be used to define a completeArbitraryinstance for a bounded enumeration data type.For example, let's say we have the following (admittedly contrived) type:
We can then define the following
Arbitraryinstance:Since
shrinkBoundedEnumreusesshrinkIntegralinternally, we get similar shrinking behaviour: values earlier in the shrink list are shrunk more aggressively, followed by the usual exponential back-off: