GHC.Internal.Data.Enum

Successor of a value. For numeric types, succ adds 1.

Predecessor of a value. For numeric types, pred subtracts 1.

Convert from an Int.

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.

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]

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]

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] = []

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] = []