Module State.M2Source

M2 is a basic implementation of S2 (state monad with variable state type).

include Base.Monad.S2
Sourcetype ('a, 'e) t
Sourceval (>>=) : ('a, 'e) t -> ('a -> ('b, 'e) t) -> ('b, 'e) t
Sourceval (>>|) : ('a, 'e) t -> ('a -> 'b) -> ('b, 'e) t
Sourcemodule Let_syntax : sig ... end
Sourcemodule Monad_infix : sig ... end

Same as Infix, except the monad type has two arguments. The second is always just passed through.

Sourceval bind : ('a, 'e) t -> f:('a -> ('b, 'e) t) -> ('b, 'e) t
Sourceval map : ('a, 'e) t -> f:('a -> 'b) -> ('b, 'e) t
Sourceval join : (('a, 'e) t, 'e) t -> ('a, 'e) t
Sourceval ignore_m : (_, 'e) t -> (unit, 'e) t
Sourceval all : ('a, 'e) t list -> ('a list, 'e) t
Sourceval all_unit : (unit, 'e) t list -> (unit, 'e) t
include Generic with type ('a, 's) t := ('a, 's) t and type 's state := 's and type 'a final := 'a

State monads share the signatures of their builder functions with state transformers...

include State_transform_intf.Generic_builders with type ('a, 's) t := ('a, 's) t with type 's state := 's with type 'a final := 'a
include State_transform_intf.Generic_types with type ('a, 's) t := ('a, 's) t with type 's state := 's with type 'a final := 'a
Sourceval make : ('s -> 's * 'a) -> ('a, 's) t

make creates a context-sensitive computation that can modify both the current context and the data passing through.

Specialised builders

Sourceval peek : ('s -> 'a) -> ('a, 's) t

peek creates a context-sensitive computation that can look at the current context, but not modify it.

Sourceval modify : ('s -> 's) -> (Base.unit, 's) t

modify creates a context-sensitive computation that can look at and modify the current context.

Sourceval return : 'a -> ('a, 's) t

return lifts a value or monad into a stateful computation.

...as well as their runner functions...

include State_transform_intf.Generic_runners with type ('a, 's) t := ('a, 's) t and type 'a final := 'a and type 's state := 's
include State_transform_intf.Generic_types with type ('a, 's) t := ('a, 's) t with type 'a final := 'a with type 's state := 's
Sourceval run' : ('a, 's) t -> 's -> 's * 'a

run' unfolds a t into a function from context to final state and result.

Sourceval run : ('a, 's) t -> 's -> 'a

run unfolds a t into a function from context to final result. To get the final context, use run' or call peek at the end of the computation.

...and fixed-point combinators.

include State_transform_intf.Fix with type ('a, 's) t := ('a, 's) t
Sourceval fix : f:(('a -> ('a, 's) t) -> 'a -> ('a, 's) t) -> 'a -> ('a, 's) t

fix ~f init builds a fixed point on f.

At each step, f is passed a continuation mu and a value a. It may choose to return a recursive application of mu, or some value derived from a.

To begin with, f is applied to mu and init.