Test.LeanCheck.Function.List

This module is part of LeanCheck, a simple enumerative property-based testing library.

This module exports functions to convert functions to lists of return values and producing comparisons between functions.

Documentation

funToList :: Listable a => (a -> b) -> [b]

Converts a function to a list of result values for each Listable argument value.

> list  ::  [Bool]
[False,True]
> funToList not
[True,False]

> list  ::  [(Bool,Bool)]
[(False,False),(False,True),(True,False),(True,True)]
> funToList $ uncurry (&&)
[False,False,False,True]

This function may return an infinite list, use take as required.

> take 10 $ list  ::  [Int]
[0,1,-1,2,-2,3,-3,4,-4,5]
> take 10 $ funToList (+1)  ::  [Int]
[1,2,0,3,-1,4,-2,5,-3,6]

funToListMaybe :: Listable a => (a -> b) -> [Maybe b]

Converts a function to a list of Just result values or Nothing on error.

> take 6 $ funToListMaybe $ head :: [Maybe Int]
[Nothing,Just 0,Just 0,Just 1,Just 0,Just 0]

This uses errorToNothing and consequently unsafePerformIO.

funToListEither :: Listable a => (a -> b) -> [Either String b]

Converts a function to a list of Just result values or Nothing on error.

> take 6 $ funToListEither $ head :: [Either String Int]
[Left "Prelude.head: empty list",Right 0,Right 0,Right 1,Right 0,Right 0]

This uses errorToLeft and consequently unsafePerformIO.

areEqualFor :: (Listable a, Eq b) => Int -> (a -> b) -> (a -> b) -> Bool

This function can be used to define an Eq instance for functions based on testing and equality of returned values, like so:

instance (Listable a, Eq b) => Eq (a -> b) where
  (==)  =  areEqualFor 12

This catches errors and undefined values and treats them as equal.

compareFor :: (Listable a, Ord b) => Int -> (a -> b) -> (a -> b) -> Ordering

This function can be used to define an Ord instance for functions based on testing and ordering of returned values, like so:

instance (Listable a, Ord b) => Ord (a -> b) where
  compare  =  compareFor 12

This catches errors and undefined values and treats them as equal.