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fp-ts-numerics

Enum.Bounded overview

Added in v1.0.0

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utils

BoundedEnum (interface)

Type class for finite enumerations.

This should not be considered a part of a numeric hierarchy, as in Haskell. Rather, this is a type class for small, ordered sum types with statically-determined cardinality and the ability to easily compute successor and predecessor elements like DayOfWeek.

Laws:

  • succ bottom >>= succ >>= succ ... succ [cardinality - 1 times] == top
  • pred top >>= pred >>= pred ... pred [cardinality - 1 times] == bottom
  • forall a > bottom: pred a >>= succ == Just a
  • forall a < top: succ a >>= pred == Just a
  • forall a > bottom: fromEnum <$> pred a = pred (fromEnum a)
  • forall a < top: fromEnum <$> succ a = succ (fromEnum a)
  • e1 `compare` e2 == fromEnum e1 `compare` fromEnum e2
  • toEnum (fromEnum a) = Just a

Signature

export interface BoundedEnum<A> extends Bounded<A>, Enum<A> {
  /** The number of discrete value in a type.
   *
   *  E.g.
   *
   */
  cardinality: Cardinality<A>
  toEnum(int: Int32): Option<A>
  fromEnum(a: A): Int32
}

Added in v1.0.0

defaultCardinality

Provides a default implementation for cardinality.

Runs in O(n) where n is fromEnum(top)

Signature

export declare function defaultCardinality<A>(be: Bounded<A> & Enum<A>): Cardinality<A>

Added in v1.0.0

defaultFromEnum

Provides a default implementation for fromEnum.

  • Assumes toEnum(0) = some(bottom).
  • Cannot be used in conjuction with defaultPred.

Runs in O(n) where n is fromEnum(a).

Signature

export declare function defaultFromEnum<A>(e: Enum<A>): (a: A) => Int32

Added in v1.0.0

defaultToEnum

Provides a default implementation for toEnum.

  • Assumes fromEnum(bottom) = 0.
  • Cannot be used in conjuction with defaultNext.

Runs in O(n) where n is fromEnum(a).

Signature

export declare function defaultToEnum<A>(be: Bounded<A> & Enum<A>): (i: Int32) => Option<A>

Added in v1.0.0

fromThenTo

Signature

export declare function fromThenTo<F extends URIS, A>(
  f: Unfoldable1<F> & Functor1<F>,
  be: BoundedEnum<A>
): (from: A, then: A, to: A) => Kind<F, A>

Added in v1.0.0

toEnumWithDefaults

Like toEnum but returns the first argument if x is less than fromEnum(bottom) and the second argument if x is greater than fromEnum(top).

toEnumWithDefaults(boundedEnumBool)(false, true, (-1)) -- false
toEnumWithDefaults(boundedEnumBool)(false, true, 0)    -- false
toEnumWithDefaults(boundedEnumBool)(false, true, 1)    -- true
toEnumWithDefaults(boundedEnumBool)(false, true, 2)    -- true

Signature

export declare function toEnumWithDefaults<A>(be: BoundedEnum<A>): (low: A, high: A, n: Int32) => A

Added in v1.0.0