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io-closure.js
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48 lines (40 loc) · 1.31 KB
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'use strict';
const createIO = (effect) => ({
map: (fn) => createIO(() => fn(effect())),
chain: (fn) => fn(effect()),
run: () => effect(),
});
const createMonad = (value) => ({
map: (fn) => createMonad(fn(structuredClone(value))),
chain: (fn) => fn(structuredClone(value)),
ap: (container) => container.map(value),
});
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: ${y}`));
return errors;
};
const createPoint = (x, y) => {
const errors = validatePoint(x, y);
if (errors.length > 0) {
const cause = new AggregateError(errors, 'Validation');
throw new RangeError('Bad coordinates', { cause });
}
return { x, y };
};
const move = (delta) => (point) => ({
x: point.x + delta.x,
y: point.y + delta.y,
});
const clone = (point) => ({ ...point });
const toString = (point) => `(${point.x}, ${point.y})`;
// Usage
const readPoint = () => createIO(() => createPoint(10, 20));
const writeLine = (text) => createIO(() => console.log(text));
const p1 = readPoint().map(createMonad).run();
p1.map(toString).chain(writeLine).run();
const c0 = p1.map(clone);
const t1 = createMonad(move({ x: -5, y: 10 }));
const c1 = t1.ap(c0);
c1.map(toString).chain(writeLine).run();