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1. enumFromThen :: Enum a => a -> a -> [a]

   constrained-categories	Control.Category.Constrained.Prelude

   Used in Haskell's translation of [n,n'..] with [n,n'..] = enumFromThen n n', a possible implementation being enumFromThen n n' = n : n' : worker (f x) (f x n'), worker s v = v : worker s (s v), x = fromEnum n' - fromEnum n and

   f n y
   | n > 0 = f (n - 1) (succ y)
   | n < 0 = f (n + 1) (pred y)
   | otherwise = y
   
   

   Examples

   • enumFromThen 4 6 :: [Integer] = [4,6,8,10...]

   • enumFromThen 6 2 :: [Int] = [6,2,-2,-6,...,minBound ::
     Int]

2. enumFromThenTo :: Enum a => a -> a -> a -> [a]

   constrained-categories	Control.Category.Constrained.Prelude

   Used in Haskell's translation of [n,n'..m] with [n,n'..m] = enumFromThenTo n n' m, a possible implementation being enumFromThenTo n n' m = worker (f x) (c x) n m, x = fromEnum n' - fromEnum n, c x = bool (>=) ((x 0)

   f n y
   | n > 0 = f (n - 1) (succ y)
   | n < 0 = f (n + 1) (pred y)
   | otherwise = y
   
   

   and

   worker s c v m
   | c v m = v : worker s c (s v) m
   | otherwise = []
   
   

   Examples

   • enumFromThenTo 4 2 -6 :: [Integer] =
     [4,2,0,-2,-4,-6]

   • enumFromThenTo 6 8 2 :: [Int] = []

3. enumFromTo :: Enum a => a -> a -> [a]

   constrained-categories	Control.Category.Constrained.Prelude

   Used in Haskell's translation of [n..m] with [n..m] = enumFromTo n m, a possible implementation being

   enumFromTo n m
   | n <= m = n : enumFromTo (succ n) m
   | otherwise = []
   
   

   Examples

   • enumFromTo 6 10 :: [Int] = [6,7,8,9,10]

   • enumFromTo 42 1 :: [Integer] = []

4. fromEnum :: Enum a => a -> Int

   constrained-categories	Control.Category.Constrained.Prelude

   Convert to an Int. It is implementation-dependent what fromEnum returns when applied to a value that is too large to fit in an Int.

5. signum :: Num a => a -> a

   constrained-categories	Control.Category.Constrained.Prelude

   Sign of a number. The functions abs and signum should satisfy the law:

   abs x * signum x == x
   

   For real numbers, the signum is either -1 (negative), 0 (zero) or 1 (positive).

6. toEnum :: Enum a => Int -> a

   constrained-categories	Control.Category.Constrained.Prelude

   Convert from an Int.

7. class Enum a

   constrained-categories	Control.Category.Hask

   Class Enum defines operations on sequentially ordered types. The enumFrom... methods are used in Haskell's translation of arithmetic sequences. Instances of Enum may be derived for any enumeration type (types whose constructors have no fields). The nullary constructors are assumed to be numbered left-to-right by fromEnum from 0 through n-1. See Chapter 10 of the Haskell Report for more details. For any type that is an instance of class Bounded as well as Enum, the following should hold:

   • The calls succ maxBound and pred minBound should result in a runtime error.
   • fromEnum and toEnum should give a runtime error if the result value is not representable in the result type. For example, toEnum 7 :: Bool is an error.
   • enumFrom and enumFromThen should be defined with an implicit bound, thus:

   enumFrom     x   = enumFromTo     x maxBound
   enumFromThen x y = enumFromThenTo x y bound
   where
   bound | fromEnum y >= fromEnum x = maxBound
   | otherwise                = minBound
   

8. enumFrom :: Enum a => a -> [a]

   constrained-categories	Control.Category.Hask

   Used in Haskell's translation of [n..] with [n..] = enumFrom n, a possible implementation being enumFrom n = n : enumFrom (succ n).

   Examples

   • enumFrom 4 :: [Integer] = [4,5,6,7,...]

   • enumFrom 6 :: [Int] = [6,7,8,9,...,maxBound ::
     Int]

9. enumFromThen :: Enum a => a -> a -> [a]

   constrained-categories	Control.Category.Hask

   Used in Haskell's translation of [n,n'..] with [n,n'..] = enumFromThen n n', a possible implementation being enumFromThen n n' = n : n' : worker (f x) (f x n'), worker s v = v : worker s (s v), x = fromEnum n' - fromEnum n and

   f n y
   | n > 0 = f (n - 1) (succ y)
   | n < 0 = f (n + 1) (pred y)
   | otherwise = y
   
   

   Examples

   • enumFromThen 4 6 :: [Integer] = [4,6,8,10...]

   • enumFromThen 6 2 :: [Int] = [6,2,-2,-6,...,minBound ::
     Int]

10. enumFromThenTo :: Enum a => a -> a -> a -> [a]

    constrained-categories	Control.Category.Hask

    Used in Haskell's translation of [n,n'..m] with [n,n'..m] = enumFromThenTo n n' m, a possible implementation being enumFromThenTo n n' m = worker (f x) (c x) n m, x = fromEnum n' - fromEnum n, c x = bool (>=) ((x 0)

    f n y
    | n > 0 = f (n - 1) (succ y)
    | n < 0 = f (n + 1) (pred y)
    | otherwise = y
    
    

    and

    worker s c v m
    | c v m = v : worker s c (s v) m
    | otherwise = []
    
    

    Examples

    • enumFromThenTo 4 2 -6 :: [Integer] =
      [4,2,0,-2,-4,-6]

    • enumFromThenTo 6 8 2 :: [Int] = []

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