Range.hs

-- | Internal 'Range' API
module Test.Falsify.Internal.Range (
    -- * Definition
    Range(..)
  ) where

import Data.List.NonEmpty (NonEmpty)

import Test.Falsify.Reexported.Generator.Precision

{-------------------------------------------------------------------------------
  Definition
-------------------------------------------------------------------------------}

-- | Range of values
data Range a where
  -- | Constant (point) range
  Constant :: a -> Range a

  -- | Construct value from 'WordN' of the given precision
  --
  -- This is the main constructor for 'Range'.
  --
  -- Typically this 'WordN' is used to construct a fraction which is then used
  -- to index the range (see 'fromProperFraction'), though some generators use
  -- the 'WordN' directly.
  FromWordN :: Precision -> (WordN -> a) -> Range a

  -- | Evaluate each range and choose the \"smallest\"
  --
  -- Each value in the range is annotated with some distance metric; for
  -- example, this could be the distance to some predefined point (e.g. as in
  -- 'Test.Falsify.Range.towards')
  Smallest :: Ord b => NonEmpty (Range (a, b)) -> Range a

deriving stock instance Functor Range