TypeScript compatibility

The stable version is tested against TypeScript 3.1.6, but should run with TypeScript 2.8.0+ too

Usage

From purescript-logging’s README

A logger receives records and potentially performs some effects. You can create a logger from any function (a: A) => HKT<M, void> for any A and M.

Unlike most other logging libraries, logging-ts has no separate concepts “loggers” and “handlers”. Instead, loggers can be composed into larger loggers using the Semigroup instance. Loggers can also be transformed using contramap (for transforming records) and filter (for filtering records). An example use case might be the following:

import { io } from 'fp-ts/lib/IO'
import * as L from 'logging-ts'
import * as C from 'fp-ts/lib/Console'
import * as D from 'fp-ts/lib/Date'

type Level = 'Debug' | 'Info' | 'Warning' | 'Error'

interface Entry {
  message: string
  time: Date
  level: Level
}

const showEntry = (entry: Entry): string => `[${entry.level}] ${entry.time.toLocaleString()} ${entry.message}`

const getEntryLogger = (prefix: string) => {
  return new L.Logger((entry: Entry) => C.log(`${prefix}: ${showEntry(entry)}`))
}

const filter = L.filter(io)
const debugLogger = filter(getEntryLogger('debug.log'), e => e.level === 'Debug')
const productionLogger = filter(getEntryLogger('production.log'), e => e.level !== 'Debug')
const logger = L.getSemigroup(io)<Entry>().concat(debugLogger, productionLogger)

const log = L.log(logger)

const info = (message: string) => (time: Date) => log({ message, time, level: 'Info' })
const debug = (message: string) => (time: Date) => log({ message, time, level: 'Debug' })

const program = D.create
  .chain(info('boot'))
  .chain(() => D.create)
  .chain(debug('Hello!'))

program.run()
/*
production.log: [Info] 2017-10-17 10:14:21 boot
debug.log: [Debug] 2017-10-17 10:14:21 Hello!
*/