package preface

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Type
Implementation
1. Functor
2. Applicative
3. Alternative
4. Selective
5. Monad
6. Monad Plus
7. Foldable
8. Invariant Functor
9. Monoid
Additional functions
1. Producing Option
2. Composing Option

Module `Preface_stdlib.Option`Source

Implementation for Option.t.

Option.t allows to explicitly describe the presence (Some x) or absence (None) of a value. This allows, among other things, the transformation of partial functions into total functions, and forces the explicit handling of the case where None is returned.

Type

Sourcetype 'a t = 'a option

Implementation

The set of concrete implementations for Option.t.

Functor

module Functor : Preface_specs.FUNCTOR with type 'a t = 'a t

Applicative

Option.t implements Preface_specs.APPLICATIVE and introduces an interface to define Preface_specs.TRAVERSABLE using Option as an iterable structure.

module Applicative : 
  Preface_specs.Traversable.API_OVER_APPLICATIVE with type 'a t = 'a t

Alternative

module Alternative : Preface_specs.ALTERNATIVE with type 'a t = 'a t

Selective

module Selective : Preface_specs.SELECTIVE with type 'a t = 'a t

Monad

Option.t implements Preface_specs.MONAD and introduces an interface to define Preface_specs.TRAVERSABLE using Option as an iterable structure.

module Monad : Preface_specs.Traversable.API_OVER_MONAD with type 'a t = 'a t

Monad Plus

module Monad_plus : Preface_specs.MONAD_PLUS with type 'a t = 'a t

Foldable

module Foldable : Preface_specs.FOLDABLE with type 'a t = 'a t

Invariant Functor

module Invariant : Preface_specs.INVARIANT with type 'a t = 'a t

Monoid

Option is the Free monoid over a semigroup so wrapping a Preface_specs.SEMIGROUP into an Option gives us a Preface_specs.MONOID with None as a neutral element.

Source

module Monoid
  (M : Preface_specs.SEMIGROUP) : 
  Preface_specs.MONOID with type t = M.t t

Additional functions

Additional functions to facilitate practical work with Option.t.

Sourceval pure : 'a -> 'a t

Create a value from 'a to 'a Option.t.

Sourceval equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool

Equality between Option.t.

Sourceval pp : (Format.formatter -> 'a -> unit) -> Format.formatter -> 'a t -> unit

Formatter for pretty-printing for Option.t.

Producing Option

Sourceval if_ : 'a Predicate.t -> 'a -> 'a t

is_ p x produces Some x if p x is true, otherwise, it produces None.

Sourceval unless : 'a Predicate.t -> 'a -> 'a t

is_ p x produces Some x if p x is false, otherwise, it produces None.

Composing Option

Sourceval or_ : 'a t -> 'a t -> 'a t

or_ a b returns a if a is Some x else it returns b. Equivalent to Alternative.combine.