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Within LTS Haskell 24.46 (ghc-9.10.3)
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base Prelude 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
enumFrom :: Enum a => a -> [a]base Prelude 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]
enumFromThen :: Enum a => a -> a -> [a]base 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]
enumFromThenTo :: Enum a => a -> a -> a -> [a]base 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
andworker 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] = []
enumFromTo :: Enum a => a -> a -> [a]base 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] = []
fromEnum :: Enum a => a -> Intbase 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.
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base 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). -
base Prelude Convert from an Int.
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base Control.Concurrent Returns the number of Haskell threads that can run truly simultaneously (on separate physical processors) at any given time. To change this value, use setNumCapabilities.
setNumCapabilities :: Int -> IO ()base Control.Concurrent Set the number of Haskell threads that can run truly simultaneously (on separate physical processors) at any given time. The number passed to forkOn is interpreted modulo this value. The initial value is given by the +RTS -N runtime flag. This is also the number of threads that will participate in parallel garbage collection. It is strongly recommended that the number of capabilities is not set larger than the number of physical processor cores, and it may often be beneficial to leave one or more cores free to avoid contention with other processes in the machine.