coplt/suspend.js

Kotlin like suspend continuity

Suspend.js

Experimental suspend base support library, to support continuations like kotlin suspend

This library is for theoretical research

It is not recommended that you actually use this library

Examples

MaybeMonad

import { Continue, Suspend, ReadySuspend } from '@coplt/suspend'

type Maybe<T> = { val: T } | null

namespace Maybe {
    export function maybe<R>(f: (co: Continue<R, Maybe<R>>) => Suspend<Maybe<R>>): Maybe<R> {
        return Suspend.calc(f(new Continue(val => new ReadySuspend({ val }))))
    }

    export function bind<T, R>(m: Maybe<T>, co: Continue<T, Maybe<R>>): Suspend<Maybe<R>> {
        if (m == null) return new ReadySuspend(null)
        return co.suspend(m.val)
    }
}

• Usage 1

  let i = 0
  const r = Maybe.maybe<string>(co => {
      i++
      console.log(1)
      return Maybe.bind(
          { val: 1 },
          new Continue(a => {
              i++
              console.log(2)
              return co.suspend(`${a}`)
          })
      )
  })
  expect(i).toBe(2)
  expect(r).toEqual({ val: '1' })
  // console.log: 1 2

  fake code using suspend sugar

  let i = 0
  const r = Maybe.maybe<string>(suspend () => {
      i++
      console.log(1)
      const a = Maybe.bind({ val: 1 })
      i++
      console.log(2)
      return `${a}`
  })
  expect(i).toBe(2)
  expect(r).toEqual({ val: '1' })
  // console.log: 1 2

• Usage 2

  let i = 0
  const r = Maybe.maybe<string>(co => {
      i++
      console.log(1)
      return Maybe.bind(
          null, // return here
          new Continue(a => {
              i++
              console.log(2)
              return co.suspend(`${a}`)
          })
      )
  })
  expect(i).toBe(1)
  expect(r).toEqual(null)
  // console.log: 1

  fake code using suspend sugar

  let i = 0
  const r = Maybe.maybe<string>(suspend () => {
      i++
      console.log(1)
      const a = Maybe.bind(null) // return here
      i++
      console.log(2)
      return `${a}`
  })
  expect(i).toBe(1)
  expect(r).toEqual(null)
  // console.log: 1

Async

import { Async, Continue } from '@coplt/suspend'

function delay(ms: number) {
    return new Promise<void>(res => {
        setTimeout(res, ms)
    })
}

• Usage 1

  const r = await Async.run<number>(co => {
      return Async.await(
          delay(0), // any Promise value
          new Continue(() => {
              return co.suspend(1)
          })
      )
  })
  expect(r).toBe(1)

  fake code using suspend sugar

   const r = await Async.run<number>(suspend () => {
      Async.await(delay(0)) // any Promise value
      return 1
  })
  expect(r).toBe(1)

• Usage 2

  const r = await Async.run<number>(co => {
      return Async.delay(
          0,
          new Continue(() => {
              return co.suspend(1)
          })
      )
  })
  expect(r).toBe(1)

  fake code using suspend sugar

  const r = await Async.run<number>(suspend () => {
      Async.delay(0)
      return 1
  })
  expect(r).toBe(1)

• Usage Throw 1

  try {
      await Async.run<number>(() => {
          return Async.delay(
              0,
              new Continue(() => {
                  throw 'err'
              })
          )
      })
      throw 'never'
  } catch (e) {
      expect(e).toBe('err')
  }

  fake code using suspend sugar

  try {
      await Async.run<number>(suspend () => {
          Async.delay(0)
          throw 'err'
      })
      throw 'never'
  } catch (e) {
      expect(e).toBe('err')
  }

• Usage Throw 2

  await Async.run<number>(co => {
      if (Math.random() > 0.5) throw 'err'
      return Async.delay(
          0,
          new Continue(() => {
              return co.suspend(1)
          })
      )
  })

  fake code using suspend sugar

  await Async.run<number>(suspend () => {
      if (Math.random() > 0.5) throw 'err'
      Async.delay(0)
      return 1
  })

Seq

function* take<T>(n: number, iter: Iterable<T>): Iterable<T> {
    let i = 0
    for (const v of iter) {
        if (i >= n) return
        yield v
        i++
    }
}

• Usage 1

  const r = [
      ...Sequence.seq<number>((ctx, co) => {
          return ctx.yield(
              1,
              new Continue(() => {
                  return ctx.yield(
                      2,
                      new Continue(() => {
                          return ctx.yield(3, co)
                      })
                  )
              })
          )
      }),
  ]
  expect(r).toEqual([1, 2, 3])

  fake code using suspend sugar

  const r = [
      ...Sequence.seq<number>(suspend ctx => {
          ctx.yield(1)
          ctx.yield(2)
          ctx.yield(3)
      }),
  ]
  expect(r).toEqual([1, 2, 3])

• Usage 2

  const r = [
      ...Sequence.seq<number>((ctx, co) => {
          return ctx.yieldAll([1, 2, 3], co)
      }),
  ]
  expect(r).toEqual([1, 2, 3])

  fake code using suspend sugar

  const r = [
      ...Sequence.seq<number>(suspend ctx => {
          ctx.yieldAll([1, 2, 3])
      }),
  ]
  expect(r).toEqual([1, 2, 3])

• Usage 3

  function fib(n: number) {
      return Sequence.seq<number>((ctx, co) => {
          let [i, x, y] = [0, 0, 1]
          const loop = (): Suspend<void> => {
              if (i >= n) return co.suspend(void 0)
              return ctx.yield(
                  y,
                  new Continue(() => {
                      ;[x, y] = [y, x + y]
                      i++
                      return loop()
                  })
              )
          }
          return loop()
      })
  }
  
  const r = [...fib(10)]
  expect(r).toEqual([1, 1, 2, 3, 5, 8, 13, 21, 34, 55])

  fake code using suspend sugar

  function fib(n: number) {
      return Sequence.seq<number>(suspend ctx => {
          let [i, x, y] = [0, 0, 1]
          for (;;) {
              if (i >= n) return
              ctx.yield(y)
              ;[x, y] = [y, x + y]
              i++
          }
      })
  }
  
  const r = [...fib(10)]
  expect(r).toEqual([1, 1, 2, 3, 5, 8, 13, 21, 34, 55])

• Usage 4

  function partA(ctx: Sequence<number>, co: Continue<void>): Suspend<void> {
      return ctx.yield(1, new Continue(() => partB(ctx, co)))
  }
  function partB(ctx: Sequence<number>, co: Continue<void>): Suspend<void> {
      return ctx.yield(2, new Continue(() => partA(ctx, co)))
  }
  
  const r = [...take(5, Sequence.seq(partA))]
  expect(r).toEqual([1, 2, 1, 2, 1])

  fake code using suspend sugar

  suspend function partA(ctx: Sequence<number>): void {
      ctx.yield(1)
      return partB(ctx)
  }
  suspend function partB(ctx: Sequence<number>): void {
      ctx.yield(2)
      return partA(ctx)
  }
  
  const r = [...take(5, Sequence.seq(partA))]
  expect(r).toEqual([1, 2, 1, 2, 1])