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maybe.js
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maybe.js
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"use strict";
var Just = require("./just.js");
var Nothing = require("./nothing.js");
var brand = {};
Object.assign(MaybeJust,Just);
Object.assign(MaybeNothing,Nothing);
module.exports = Object.assign(Maybe,{
Just: MaybeJust, Nothing: MaybeNothing, of: Maybe,
pure: Maybe, unit: Maybe, is, from,
});
// **************************
function MaybeJust(val) {
return Maybe(val);
}
function MaybeNothing() {
return Maybe(Nothing());
}
function Maybe(val) {
var mn = val;
var isJust = MaybeJust.is(mn);
var isNothing = MaybeNothing.is(mn);
if (!(isJust || isNothing)) {
mn = Just(val);
isJust = true;
}
else if (isJust) {
// intentional monad violation, to extract its value
val = mn.chain(v => v);
}
// isNothing
else {
val = void 0;
}
var publicAPI = {
map, chain, flatMap: chain, bind: chain,
ap, concat, fold, _inspect, _is,
get [Symbol.toStringTag]() {
return `Maybe:${mn[Symbol.toStringTag]}`;
},
};
return publicAPI;
// *********************
function map(fn) {
return (isJust ? Maybe(mn.map(fn)) : publicAPI);
}
function chain(fn) {
return (isJust ? mn.chain(fn) : publicAPI);
}
function ap(m) {
return (isJust ? m.map(val) : publicAPI);
}
function concat(m) {
return (isJust ? m.map(v => val.concat(v)) : publicAPI);
}
function fold(asNothing,asJust) {
return (isJust ? asJust(val) : asNothing(val));
}
function _inspect() {
var v = isJust ? mn._inspect().match(/^Just\((.*)\)$/)[1] : "";
return `${publicAPI[Symbol.toStringTag]}(${ v })`;
}
function _is(br) {
return br === brand || mn._is(br);
}
}
function is(val) {
return val && typeof val._is == "function" && val._is(brand);
}
function from(val) {
return MaybeNothing.isEmpty(val) ? MaybeNothing() : Maybe(val);
}