34 lines
1.2 KiB
JavaScript
34 lines
1.2 KiB
JavaScript
/**
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* The `Alternative` type class extends the `Alt` type class with a value that should be the left and right identity for `alt`.
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*
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* It is similar to `Monoid`, except that it applies to types of kind `* -> *`, like `Array` or `Option`, rather than
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* concrete types like `string` or `number`.
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*
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* `Alternative` instances should satisfy the following laws:
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*
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* 1. Left identity: `A.alt(zero, fa) <-> fa`
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* 2. Right identity: `A.alt(fa, zero) <-> fa`
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* 3. Annihilation: `A.map(zero, f) <-> zero`
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* 4. Distributivity: `A.ap(A.alt(fab, gab), fa) <-> A.alt(A.ap(fab, fa), A.ap(gab, fa))`
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* 5. Annihilation: `A.ap(zero, fa) <-> zero`
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*
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* @since 2.0.0
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*/
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import { altAll as altAll_ } from './Alt';
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import { getApplySemigroup } from './Apply';
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export function altAll(F) {
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return altAll_(F)(F.zero());
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}
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export function getAlternativeMonoid(F) {
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var f = getApplySemigroup(F);
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return function (S) {
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var SF = f(S);
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return {
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concat: function (first, second) {
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return F.alt(SF.concat(first, second), function () { return F.alt(first, function () { return second; }); });
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},
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empty: F.zero()
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};
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};
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}
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