1	import Base
2	
3	# The existential field retains the actual typed owner header across a pure
4	# call. Its native layout stays boxed even when the held product is wide.
5	# Bind the header before that call: native ANF hoists nested call arguments
6	# before inline constructor arguments, otherwise retaining the unpacked owners.
7	type Header<-Input:Type,-Output:Type> is Type:
8	  Header{-Held:Type,held:Held,resume:Held -> Input -> Output}
9	def returned(-Input:Type,-Output:Type,header:Header<Input,Output>,value:Input) -> Output:
10	  match header:
11	    case Header{Held,held,resume}:resume(held,value)
12	def decided(-Output:Type,header:Header<(Bool & Bool),Output>,valid:Bool,compatible:Bool) -> Output:
13	  returned(Bool & Bool,Output,header,(valid,compatible))
14	
15	# A unary resume receives both actual owners together, avoiding a curried
16	# closure that captures the unpacked Held before receiving Input.
17	type PairedHeader<-Input:Type,-Output:Type> is Type:
18	  PairedHeader{-Held:Type,held:Held,resume:(Held & Input) -> Output}
19	def paired_returned(-Input:Type,-Output:Type,header:PairedHeader<Input,Output>,value:Input) -> Output:
20	  match header:
21	    case PairedHeader{Held,held,resume}:resume((held,value))
22	def pure_paired(-Output:Type,header:PairedHeader<Unit,Output>) -> IO(Output):
23	  R => k => k(paired_returned(Unit,Output,header,Unit{}))