Module type State.API

The complete interface of a State monad which introduces the Monad API into the State API.

type state

The encapsulated state.

type 'a monad

The inner monad.

type 'a t = state -> ('a * state) monad

The type held by the state monad.

val upper : 'a monad -> 'a t

promote monad into the transformation.

val eval : 'a t -> state -> 'a monad

Unwrap the state computation and extract the current value.

val exec : 'a t -> state -> state monad

Unwrap the state computation and extract the current state.

val run : 'a t -> state -> ('a * state) monad

Unwrap the state computation.

val state : (state -> 'a * state) -> 'a t

Lift a function into a state.

val get : state t

Returns the current state.

val set : state -> unit t

Replace the state with the given one.

val modify : (state -> state) -> unit t

Modify the state applying the given function.

val gets : (state -> 'a) -> 'a t

Apply a function to the current state and return it.

Monad

module Monad : Monad.API

Type

Type
Functions
include Indexed_monad.WITH_RETURN with type ('a, 'index) t := 'a t
include Indexed_bind.WITH_BIND with type ('a, 'index) t := 'a t
val bind : ('a -> 'b t) -> 'a t -> 'b t

bind f m passes the result of computation m to function f.

include Indexed_monad.WITH_RETURN with type ('a, 'index) t := 'a t
include Indexed_bind.WITH_MAP_AND_JOIN with type ('a, 'index) t := 'a t
val map : ('a -> 'b) -> 'a t -> 'b t

Mapping over from 'a to 'b.

val join : 'a t t -> 'a t

join remove one level of monadic structure, projecting its bound argument into the outer level.

include Indexed_monad.WITH_RETURN with type ('a, 'index) t := 'a t
val return : 'a -> 'a t

Lift a value into a t.

include Indexed_bind.WITH_KLEISLI_COMPOSITION with type ('a, 'index) t := 'a t
val compose_left_to_right : ('a -> 'b t) -> ('b -> 'c t) -> 'a -> 'c t

Composing monadic functions using Kleisli Arrow (from left to right).

val compose_right_to_left : ('b -> 'c t) -> ('a -> 'b t) -> 'a -> 'c t

Composing monadic functions using Kleisli Arrow (from right to left).

val lift : ('a -> 'b) -> 'a t -> 'b t

Mapping over t from 'a to 'b.

val lift2 : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t

Lift a binary function that acts on arbitrary values into a function that acts t values.

val lift3 : ('a -> 'b -> 'c -> 'd) -> 'a t -> 'b t -> 'c t -> 'd t

Lift a ternary function that acts on arbitrary values into a function that acts t values.

val replace : 'a -> 'b t -> 'a t

Create a new t, replacing all values of the given functor by given a value of 'a.

val void : 'a t -> unit t

Create a new t, replacing all values in the given functor by unit.

Infix operators
module Infix : Indexed_monad.INFIX with type ('a, 'index) t := 'a t
val (=|<) : ('a -> 'b) -> 'a t -> 'b t

Infix version of CORE.map.

val (>|=) : 'a t -> ('a -> 'b) -> 'b t

Infix flipped version of CORE.map.

val (>>=) : 'a t -> ('a -> 'b t) -> 'b t

Infix flipped version of CORE.bind.

val (=<<) : ('a -> 'b t) -> 'a t -> 'b t

Infix version of CORE.bind.

val (>=>) : ('a -> 'b t) -> ('b -> 'c t) -> 'a -> 'c t

Infix version of CORE.compose_left_to_right.

val (<=<) : ('b -> 'c t) -> ('a -> 'b t) -> 'a -> 'c t

Infix version of OPERATION.compose_right_to_left.

val (>>) : unit t -> 'b t -> 'b t

Sequentially compose two actions, discarding any value produced by the first.

val (<<) : 'a t -> unit t -> 'a t

Sequentially compose two actions, discarding any value produced by the second.

val (<$>) : ('a -> 'b) -> 'a t -> 'b t

Infix version of CORE.map.

val (<&>) : 'a t -> ('a -> 'b) -> 'b t

Flipped and infix version of CORE.map.

val (<$) : 'a -> 'b t -> 'a t

Infix version of OPERATION.replace.

val ($>) : 'a t -> 'b -> 'b t

Flipped and infix version of OPERATION.replace.

Syntax
module Syntax : Indexed_monad.SYNTAX with type ('a, 'index) t := 'a t
val let* : 'a t -> ('a -> 'b t) -> 'b t

Syntactic shortcuts for flipped version of CORE.bind:

let* x = e in f is equals to bind (fun x -> f) e.

val let+ : 'a t -> ('a -> 'b) -> 'b t

let operator for mapping.