Result Primitives

Railway Oriented Programming (ROP) helpers. Every Result<A, E> is either Ok<A> or Err<E> — no exceptions, no null.

import { ok, err, isOk, isErr, map, flatMap, mapErr, getOrElse } from '@uuki/schemable-validator-client'

---

ok(value) / err(error)

Construct the two variants.

import { ok, err } from '@uuki/schemable-validator-client'

const success = ok('validated value')   // Ok<string>
const failure = err(['is required'])    // Err<string[]>

---

isOk(result) / isErr(result)

Type-narrowing guards.

import { isOk, isErr } from '@uuki/schemable-validator-client'

if (isOk(result)) {
  console.log(result.value)   // narrowed to Ok<A>
}
if (isErr(result)) {
  console.log(result.error)   // narrowed to Err<E>
}

---

map(result, fn)

Transform the Ok value; pass Err through unchanged.

import { ok, err, map } from '@uuki/schemable-validator-client'

const r = ok('  hello  ')
const trimmed = map(r, (s) => s.trim())   // Ok<'hello'>
const failed  = map(err('oops'), (s) => s.trim())  // Err<'oops'>

---

flatMap(result, fn)

Chain an Ok value into another Result-returning function. Short-circuits on Err.

import { ok, err, flatMap } from '@uuki/schemable-validator-client'

const parseAge = (s: string) =>
  Number.isInteger(+s) ? ok(+s) : err('not a number')

const checkAdult = (n: number) =>
  n >= 18 ? ok(n) : err('must be at least 18')

const result = flatMap(parseAge('21'), checkAdult)  // Ok<21>
const failed = flatMap(parseAge('abc'), checkAdult) // Err<'not a number'>

---

mapErr(result, fn)

Transform the Err value; pass Ok through unchanged. Useful for translating error messages.

import { err, mapErr } from '@uuki/schemable-validator-client'

const translated = mapErr(
  err('is required'),
  (msg) => `このフィールドは${msg}`,
)
// Err<'このフィールドはis required'>

---

getOrElse(result, fallback)

Unwrap the Ok value, or return a fallback for Err.

import { ok, err, getOrElse } from '@uuki/schemable-validator-client'

getOrElse(ok('Alice'), 'unknown')    // 'Alice'
getOrElse(err('missing'), 'unknown') // 'unknown'