The Alternative
type class extends the Alt
type class with a value that should be the left and right identity for alt
.
It is similar to Monoid
, except that it applies to types of kind * -> *
, like Array
or Option
, rather than
concrete types like string
or number
.
Alternative
instances should satisfy the following laws:
A.alt(zero, fa) <-> fa
A.alt(fa, zero) <-> fa
A.map(zero, f) <-> zero
A.ap(A.alt(fab, gab), fa) <-> A.alt(A.ap(fab, fa), A.ap(gab, fa))
A.ap(zero, fa) <-> zero
Added in v2.0.0
Signature
export interface Alternative<F> extends Applicative<F>, Alt<F> {
readonly zero: <A>() => HKT<F, A>
}
Added in v2.0.0
Signature
export interface Alternative1<F extends URIS> extends Applicative1<F>, Alt1<F> {
readonly zero: <A>() => Kind<F, A>
}
Added in v2.0.0
Signature
export interface Alternative2<F extends URIS2> extends Applicative2<F>, Alt2<F> {
readonly zero: <E, A>() => Kind2<F, E, A>
}
Added in v2.0.0
Signature
export interface Alternative2C<F extends URIS2, E> extends Applicative2C<F, E>, Alt2C<F, E> {
readonly zero: <A>() => Kind2<F, E, A>
}
Added in v2.0.0
Signature
export interface Alternative3<F extends URIS3> extends Applicative3<F>, Alt3<F> {
readonly zero: <R, E, A>() => Kind3<F, R, E, A>
}
Added in v2.0.0