Add a conservative metadata fixer for missing risk and source fields, cover it with tests, and backfill the remaining skills using explicit source inference only when the provenance is clear. Fall back to the repo-documented defaults when the file does not support a stronger claim. Refs #365
2.0 KiB
2.0 KiB
name, description, risk, source, version, tags
| name | description | risk | source | version | tags | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| fp-either-ref | Quick reference for Either type. Use when user needs error handling, validation, or operations that can fail with typed errors. | unknown | community | 1.0.0 |
|
Either Quick Reference
Either = success or failure. Right(value) or Left(error).
Create
import * as E from 'fp-ts/Either'
E.right(value) // Success
E.left(error) // Failure
E.fromNullable(err)(x) // null → Left(err), else Right(x)
E.tryCatch(fn, toError) // try/catch → Either
Transform
E.map(fn) // Transform Right value
E.mapLeft(fn) // Transform Left error
E.flatMap(fn) // Chain (fn returns Either)
E.filterOrElse(pred, toErr) // Right → Left if pred fails
Extract
E.getOrElse(err => default) // Get Right or default
E.match(onLeft, onRight) // Pattern match
E.toUnion(either) // E | A (loses type info)
Common Patterns
import { pipe } from 'fp-ts/function'
import * as E from 'fp-ts/Either'
// Validation
const validateEmail = (s: string): E.Either<string, string> =>
s.includes('@') ? E.right(s) : E.left('Invalid email')
// Chain validations (stops at first error)
pipe(
E.right({ email: 'test@example.com', age: 25 }),
E.flatMap(d => pipe(validateEmail(d.email), E.map(() => d))),
E.flatMap(d => d.age >= 18 ? E.right(d) : E.left('Must be 18+'))
)
// Convert throwing code
const parseJson = (s: string) => E.tryCatch(
() => JSON.parse(s),
(e) => `Parse error: ${e}`
)
vs try/catch
// ❌ try/catch - errors not in types
try {
const data = JSON.parse(input)
process(data)
} catch (e) {
handleError(e)
}
// ✅ Either - errors explicit in types
pipe(
E.tryCatch(() => JSON.parse(input), String),
E.map(process),
E.match(handleError, identity)
)
Use Either when error type matters and you want to chain operations.