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fp-match.js
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45 lines (36 loc) · 1.06 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: ${y}`));
return errors;
};
const match = (variant, handlers) => handlers[variant.tag](variant);
// Implementation
const createPoint = (x, y) => {
const errors = validatePoint(x, y);
if (errors.length > 0) {
const cause = new AggregateError(errors, 'Validation');
throw new RangeError('Bad coordinates', { cause });
}
return Object.freeze({ tag: 'point', x, y });
};
const move = (instance, dx, dy) =>
match(instance, {
point: ({ x, y }) => createPoint(x + dx, y + dy),
});
const clone = (instance) =>
match(instance, {
point: ({ x, y }) => createPoint(x, y),
});
const toString = (instance) =>
match(instance, {
point: ({ x, y }) => `(${x}, ${y})`,
});
// Usage
const p1 = createPoint(10, 20);
console.log(toString(p1));
const c0 = clone(p1);
console.log(toString(c0));
const c1 = move(p1, -5, 10);
console.log(toString(c1));