Monadic traversal.
Traversable provides signatures and functors for containers and data structures that can be 'traversed': mapped across with a monadic side-effect. It resembles the Haskell Traversable typeclass, but with two differences:
map_m.Traversable_intf contains the signatures for Traversable.
include module type of Traversable_intfSignatures for monadic traversal.
As with Mappable, we define the signature of traversable structures in an arity-generic way, then specialise it for arity-0 and arity-1 types.
module type Generic = sig ... endGeneric describes monadic traversal on either an arity-0 or arity-1 type.
module type S0 = sig ... endS0 is the signature of a monadic traversal over arity-0 types.
module type S1 = sig ... endS1 is the signature of a monadic traversal over arity-1 types.
module type Basic_container0 = sig ... endBasic_container0 is the signature that traversable containers of arity 0 must implement.
module type Basic_container1 = sig ... endBasic_container1 is the signature that traversable containers of arity 1 must implement.
module type Generic_on_monad = sig ... endGeneric_on_monad extends Generic to contain various derived operators; we use it to derive the signatures of the various On_monad modules.
module type On_monad1 = sig ... endOn_monad1 extends Generic_on_monad with functionality that only works on arity-1 containers.
module type Generic_container = sig ... endGeneric_container is a generic interface for traversable containers, used to build Container0 (arity-0) and Container1 (arity-1).
module type S0_container = sig ... endS0_container is a generic interface for arity-0 traversable containers.
module type S1_container = sig ... endS1_container is a generic interface for arity-1 traversable containers. It also includes the extensions from Mappable.
Monadic traversal is sufficient to define fold, and, therefore, all of the key functionality for a Core-style container. As such, we expose functors for building traversable Core-style containers.
module Make_container0
(I : Basic_container0) :
S0_container with module Elt = I.Elt and type t := I.tMake_container0 makes a S0_container from a Basic_container0.
module Make_container1
(I : Basic_container1) :
S1_container with type 'a t := 'a I.tMake_container1 makes a S1_container from a Basic_container1.
module Chain0
(Outer : S0_container)
(Inner : S0_container with type t := Outer.Elt.t) :
S0_container with module Elt = Inner.Elt and type t := Outer.tChain0 chains two S0_container instances together, traversing each element of the outer instance with the inner instance.
module Helpers (M : Base.Monad.S) : sig ... endUtility functions for building traversals.