Data types

beginner

A data type is an abstraction that encapsulates a reusable coding pattern. Data types are generalized by one or more type parameters. Data types in Bow have Higher Kinded Type support by extending Kind.

All data types included in Bow are immutable; that is, you can only set their state during the initialization of the value. Whenever one of the methods need to change the state of the receiving value, a new copy of that value is returned. This way, we can easily reason about the behavior of our code.

Data types in Bow

The following tables summarize some of the data types included in Bow, together with a short description of their purpose.

Function-like types

Data type	Purpose
Function0<A>	Represents a constant function; one that does not receive any parameters and produces a constant value of type A.
Function1<I, O>	Represents a function that receives values of type I and produces values of type O.
Kleisli<F, D, A>	Represents a function that receives values of type D and produces values of type A wrapped in an effect F (namely, Kind<F, A>). Dual of Cokleisli.
ReaderT<F, D, A>	Equivalent to Kleisli<F, D, A>.
Reader<D, A>	Represents a ReaderT where the effect is Id.
Cokleisli<F, D, A>	Represents a function that receives values of type A wrapped in an effect F (namely, Kind<F, A>), and produces values of type D. Dual of Kleisli.
CoreaderT<F, D, A>	Equivalent to Cokleisli<F, D, A>.
Coreader<F, D, A>	Represents a CoreaderT where the effect is Id.

Core types

Data type	Purpose
Action<A>	Represents an input on a Moore machine.
ArrayK<A>	Represents an array of values of type A. It is like Array<A>; or [A], but with HKT support.
Const<A, T>	Represents a constant value of type A and a phantom type T.
CoSum<F, G, A>	Represents an action to change the selected content in a Sum value.
Day<F, G, A>	Represents the Day convolution of functors F and G.
DictionaryK<K, A>	Represents a dictionary where keys have type K and values have type A. It is like Dictionary<K, A> or [K: A], but with HKT support.
Either<A, B>	Represents the sum type of A and B; i.e., it holds a value of either one of those types.
Endo<A>	Represents an endomorphism on type A; i.e. a function where the input and output have the same type.
Eval<A>	Represents a potentially lazy value of type A.
Id<A>	Represents a value of type A with no further context.
Ior<A, B>	Represents a value of either A or B, or both values at the same time.
Moore<E, V>	Represents a Moore machine rendering items of type V and handling inputs of type E.
NonEmptyArray<A>	Represents an array of one or more elements of type A.
Option<A>	Represents a value of type A that may or may not be present. It is like Optional<A> or A?, but with HKT support.
Pairing<F, G>	Represents a relationship between Functors F and G where they can annihilate each other to yield a value.
Puller<A>	Represents an action to move the focus of a Zipper.
SetK<A>	Represents an unordered collection of unique values of type A. It is like Set<A> but with HKT support.
Sum<F, G, A>	Represents two values in the contexts of F and G, where only one of them is selected.
Trampoline<A>	Represents a recursive computation that can be converted into a loop.
Try<A>	Represents a computation that may have provided a value of type A or thrown an error.
Validated<A, B>	Represents a value that may be invalid, with an error value of type A, or a valid value of type B.
Zipper<A>	Represents an array of values that is focused at a specific position.

Transformers

Data type	Purpose
CoT<W, M, A>	Represents the dual MonadTransformer of the W Comonad, with M as the base Monad.
Co<W, A>	Represents a CoT where the base Monad is Id.
EitherT<F, A, B>	Represents an Either<A, B> nested in an arbitrary effect F.
EnvT<E, W, A>	Represents a Comonadic value that is extended with a global environment.
Env<E, A>	Represents an EnvT where the base Comonad is Id.
OptionT<F, A>	Represents an Option<A> nested in an arbitrary effect F.
StateT<F, S, A>	Represents a function that receives an effect of type S and produces a new state of the same type and an output value of type A, all wrapped in an effect of type F.
State<S, A>	Represents a StateT where the effect is Id.
StoreT<S, W, A>	Represents a Comonadic value that is extended with a focus of type S.
Store<S, A>	Represents a StoreT where the base Comonad is Id.
TracedT<M, W, A>	Represents a Comonadic value that is extended to depend in a monoidal position.
Traced<M, A>	Represents a TracedT where the base Comonad is Id.
WriterT<F, W, A>	Represents a value of type A under the effect F that produces a side stream of data of type W.