Num -package:haha -package:linear-base -package:svg-tree package:protolude

Basic numeric class. The Haskell Report defines no laws for Num. However, (+) and (*) are customarily expected to define a ring and have the following properties:

• Associativity of (+) (x + y) + z = x + (y + z)
• Commutativity of (+) x + y = y + x
• fromInteger 0 is the additive identity x + fromInteger 0 = x
• negate gives the additive inverse x + negate x = fromInteger 0
• Associativity of (*) (x * y) * z = x * (y * z)
• fromInteger 1 is the multiplicative identity x * fromInteger 1 = x and fromInteger 1 * x = x
• Distributivity of (*) with respect to (+) a * (b + c) = (a * b) + (a * c) and (b + c) * a = (b * a) + (c * a)

Note that it isn't customarily expected that a type instance of both Num and Ord implement an ordered ring. Indeed, in base only Integer and Rational do.

Extract the numerator of the ratio in reduced form: the numerator and denominator have no common factor and the denominator is positive.

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

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

• 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 For example:

• 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,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 = [] For example:

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

• enumFromThenTo 6 8 2 :: [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 = []. For example:

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

• enumFromTo 42 1 :: [Integer] = []

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.

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.

Selects alphabetic or numeric Unicode characters. Note that numeric digits outside the ASCII range, as well as numeric characters which aren't digits, are selected by this function but not by isDigit. Such characters may be part of identifiers but are not used by the printer and reader to represent numbers.

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.

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).

Convert from an Int.