1	import Base
2	import ./ordinary_app_registration_fields.bend as Stored
3	# Advanced application carrier pairing actual affine registration Token
4	# with its detached Fields. Fields alone do not replace registration authority;
5	# keep token and metadata from the same registration together.
6	type Record<S:Data,Token:Type> is Type:
7	  Record{token:Token,fields:Stored.Fields<S>}
8	# Return the record owner together with its one detached Fields entry.
9	# Does not invoke the registration, advance its cursor or read payloads.
10	def observed(~S:Data,~Token:Type,record:Record<S,Token>) -> Record<S,Token> & List<&2,Stored.Fields<S>>:
11	  match record:
12	    case Record{token,+fields}:(Record{token,fields},[fields])
13	def second(~S:Data,~Left:Type,~Right:Type,left:Left,before:List<&2,Stored.Fields<S>>,result:Right & List<&2,Stored.Fields<S>>) -> (Left & Right) & List<&2,Stored.Fields<S>>:
14	  match result:
15	    case (right,after):((left,right),List.append(&2,Stored.Fields<S>,before,after))
16	def first(~S:Data,~Left:Type,~Right:Type,rightFold:Right -> Right & List<&2,Stored.Fields<S>>,right:Right,result:Left & List<&2,Stored.Fields<S>>) -> (Left & Right) & List<&2,Stored.Fields<S>>:
17	  match result:
18	    case (left,before):second(~S,~Left,~Right,left,before,rightFold(right))
19	# Advanced metadata fold over heterogeneous owners in left/right order.
20	# Returns both owners and appended detached fields; supplied folds must
21	# preserve their owned registrations rather than fabricate authority.
22	def pair(~S:Data,~Left:Type,~Right:Type,leftFold:Left -> Left & List<&2,Stored.Fields<S>>,rightFold:Right -> Right & List<&2,Stored.Fields<S>>,owners:Left & Right) -> (Left & Right) & List<&2,Stored.Fields<S>>:
23	  match owners:
24	    case (left,right):first(~S,~Left,~Right,rightFold,right,leftFold(left))
25	# Unit-owner base metadata fold, returning the same Unit and no fields.
26	# Does not register a system or infer metadata from arbitrary owners.
27	def empty(~S:Data,unit:Unit) -> Unit & List<&2,Stored.Fields<S>>:
28	  (unit,[])
29	# Closed advanced adapter composing two metadata folds with the same
30	# owner-threading and left/right order as pair; does not execute systems.
31	def fold_pair(~S:Data,~Left:Type,~Right:Type,~left:Left -> Left & List<&2,Stored.Fields<S>>,~right:Right -> Right & List<&2,Stored.Fields<S>>,owners:Left & Right) -> (Left & Right) & List<&2,Stored.Fields<S>>:
32	  pair(~S,~Left,~Right,left,right,owners)