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monad-closure.js
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44 lines (38 loc) · 1.14 KB
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'use strict';
const validatePoint = (x, y) => {
const errors = [];
if (!Number.isFinite(x)) errors.push(new TypeError(`Invalid x: ${x}`));
if (!Number.isFinite(y)) errors.push(new TypeError(`Invalid y: ${y}`));
return errors;
};
const createPoint = (x, y) => {
const errors = validatePoint(x, y);
if (errors.length > 0) {
const cause = new AggregateError(errors, 'Validation');
throw new RangeError('Bad coordinates', { cause });
}
const map = (fn) => {
const coord = fn(x, y);
return createPoint(coord.x, coord.y);
};
const chain = (fn) => fn(x, y);
return { map, chain };
};
const pointTransform = (fn) => ({ ap: (point) => point.map(fn) });
const serialized = (data) => ({
map: (fn) => fn(data),
tap: (fn) => {
fn(data);
return serialized(data);
},
});
const move = (dx, dy) => (x, y) => ({ x: x + dx, y: y + dy });
const clone = (x, y) => ({ x, y });
const toString = (x, y) => serialized(`(${x}, ${y})`);
// Usage
const p1 = createPoint(10, 20);
p1.chain(toString).tap(console.log);
const c0 = p1.map(clone);
const t1 = pointTransform(move(-5, 10));
const c1 = t1.ap(c0);
c1.chain(toString).tap(console.log);