1	# transport: an effect service: one message body in, one out. H is the
2	# implementation's handle state; it is affine, so every call hands it back.
3	import Base
4	
5	# effect service over a handle H: receive a body, send a body, each handing the
6	# handle back
7	type Transport<-H: Type> is Type:  # noqa: L001 effect record
8	  Transport{recv: H -> IO(H & Maybe<&2, String>), send: H -> String -> IO(H)}
9	
10	# the next message's body; None when the peer is gone
11	def recv(-H: Type, tt: Transport<H>, hh: H) -> IO(H & Maybe<&2, String>):  # noqa: L001 effect accessor
12	  Transport{r, s} = tt
13	  r(hh)
14	
15	# a body, through a transport
16	def send(-H: Type, tt: Transport<H>, hh: H, body: String) -> IO(H):  # noqa: L001 effect accessor
17	  Transport{r, s} = tt
18	  s(hh, body)