package monads

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package monads
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The Reader monad.

The reader monad denotes a very limited form of effectful computation. In fact only a coeffect is allowed, i.e., a computation may depend on the state of the world, but can't change the world itself. The reader monad can be seen as a way of threading several functions with some common parameter without pollutiong the namespace with global variables. Also known as the configuration monad, since a common usage would be to use the Reader monad to pass command line arguments and program configuration.

module type S = sig ... end

The reader monad interface with the environment type fixed on the module level.

module type S2 = sig ... end

The reader monad interface with the environment type left variable.

type ('a, 'b) reader

an abstract type of reader computations

include S2 with type ('a, 'e) t = ('a, 'e) reader and type 'a m = 'a and type ('a, 'e) e = 'e -> 'a
include Trans.S1 with type ('a, 'e) t = ('a, 'e) reader with type 'a m = 'a with type ('a, 'e) e = 'e -> 'a
type ('a, 'e) t = ('a, 'e) reader
type 'a m = 'a
type ('a, 'e) e = 'e -> 'a
val lift : 'a m -> ('a, 'e) t

lifts inner monad into the resulting monad

val run : ('a, 'e) t -> ('a, 'e) e

runs the computation

val read : unit -> ('e, 'e) t

read () reads the environment.

include Monad2 with type ('a, 'e) t := ('a, 'e) t
val void : ('a, 'e) t -> (unit, 'e) t

void m computes m and discrards the result.

val sequence : (unit, 'e) t list -> (unit, 'e) t

sequence xs computes a sequence of computations xs in the left to right order.

val forever : ('a, 'e) t -> ('b, 'e) t

forever xs creates a computationt that never returns.

module Fn : sig ... end

Various function combinators lifted into the Kleisli category.

module Pair : sig ... end

The pair interface lifted into the monad.

module Triple : sig ... end

The triple interface lifted into a monad.

module Lift : sig ... end

Lifts functions into the monad.

module Exn : sig ... end

Interacting between monads and language exceptions

module Collection : sig ... end

Lifts collection interface into the monad.

module List : Collection.S with type 'a t := 'a list

The Monad.Collection.S2 interface for lists

module Seq : Collection.S with type 'a t := 'a Core_kernel.Sequence.t

The Monad.Collection.S2 interface for sequences

include Syntax.S2 with type ('a, 'e) t := ('a, 'e) t
val (>=>) : ('a -> ('b, 'e) t) -> ('b -> ('c, 'e) t) -> 'a -> ('c, 'e) t

f >=> g is fun x -> f x >>= g

val (!!) : 'a -> ('a, 'e) t

!!x is return x

val (!$) : ('a -> 'b) -> ('a, 'e) t -> ('b, 'e) t

!$f is Lift.unary f

val (!$$) : ('a -> 'b -> 'c) -> ('a, 'e) t -> ('b, 'e) t -> ('c, 'e) t

!$$f is Lift.binary f

val (!$$$) : ('a -> 'b -> 'c -> 'd) -> ('a, 'e) t -> ('b, 'e) t -> ('c, 'e) t -> ('d, 'e) t

!$$$f is Lift.ternary f

val (!$$$$) : ('a -> 'b -> 'c -> 'd -> 'e) -> ('a, 's) t -> ('b, 's) t -> ('c, 's) t -> ('d, 's) t -> ('e, 's) t

!$$$$f is Lift.quaternary f

val (!$$$$$) : ('a -> 'b -> 'c -> 'd -> 'e -> 'f) -> ('a, 's) t -> ('b, 's) t -> ('c, 's) t -> ('d, 's) t -> ('e, 's) t -> ('f, 's) t

!$$$$$f is Lift.quinary f

include Core_kernel.Monad.S2 with type ('a, 'e) t := ('a, 'e) t
val (>>=) : ('a, 'e) t -> ('a -> ('b, 'e) t) -> ('b, 'e) t
val (>>|) : ('a, 'e) t -> ('a -> 'b) -> ('b, 'e) t
module Let_syntax : sig ... end
module Monad_infix : sig ... end
val bind : ('a, 'e) t -> f:('a -> ('b, 'e) t) -> ('b, 'e) t
val return : 'a -> ('a, _) t
val map : ('a, 'e) t -> f:('a -> 'b) -> ('b, 'e) t
val join : (('a, 'e) t, 'e) t -> ('a, 'e) t
val ignore_m : (_, 'e) t -> (unit, 'e) t
val all : ('a, 'e) t list -> ('a list, 'e) t
val all_unit : (unit, 'e) t list -> (unit, 'e) t
val all_ignore : (unit, 'e) t list -> (unit, 'e) t
  • deprecated [since 2018-02] Use [all_unit]
module Syntax : Syntax.S2 with type ('a, 'e) t := ('a, 'e) t

Monadic operators, see Monad.Syntax.S2 for more.

module T1 (T : Core_kernel.T) (M : Monad) : sig ... end
module T2 (M : Monad) : sig ... end
module Make (T : Core_kernel.T) (M : Monad) : S with type 'a t := 'a T1(T)(M).t and type 'a m := 'a T1(T)(M).m and type 'a e := 'a T1(T)(M).e and type env := T.t

Make(Env)(M) concretizes the environment type to Env.t and composes the Reader monad with M.

module Make2 (M : Monad) : S2 with type ('a, 'e) t := ('a, 'e) T2(M).t and type 'a m := 'a T2(M).m and type ('a, 'e) e := ('a, 'e) T2(M).e

Make2(Env)(M) composes the Reader monad with M.

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