IO.within: def of Base
Import: import Base
Lines 295-302 of Base/base.bend: https://jend.leeeet.dev/read.txt?path=Base/base.bend&start_line=295&end_line=302

import Base

# Some{x} if act answers x within ms milliseconds, else None{}. The loser
# is not cancelled: it runs to its end before the program exits.
def IO.within(-A: Type, ms: U32, act: IO(A)) -> IO(Maybe<&1, A>):
  won = IO.bind(A, Maybe<&1, A>, act, x => IO.pure(Maybe<&1, A>, Some{x}))
  late = IO.bind(Unit, Maybe<&1, A>, IO.sleep(ms), u => IO.pure(Maybe<&1, A>, None{}))
  both = IO.bind(Chan(Maybe<&1, A>), Chan(Maybe<&1, A>), IO.fork(Maybe<&1, A>, won),
    IO.fork.go(Maybe<&1, A>, late))
  IO.bind(Chan(Maybe<&1, A>), Maybe<&1, A>, both, c => IO.join(Maybe<&1, A>, c))

Uses (11):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Chan
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.bind
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.fork
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.fork.go
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.join
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.pure
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.sleep
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Unit