1	import Base
2	import ./trace_facts.bend as Facts
3	
4	# Each staged command owns its payload once. Trusted raw callbacks stay opaque.
5	type Command<W:Type> is Type:
6	  Raw{apply:W -> W}
7	  Observed{apply:Facts.State -> W -> W & Facts.State}
8	def run(~W:Type,command:Command<W>,world:W,trace:Facts.State) -> W & Facts.State:
9	  match command:
10	    case Raw{apply}:(apply(world),trace)
11	    case Observed{apply}:apply(trace,world)
12	def world_only(~W:Type,result:W & Facts.State) -> W:
13	  match result:
14	    case (world,_):world
15	def run_disabled(~W:Type,command:Command<W>,world:W) -> W:
16	  world_only(~W,run(~W,command,world,Facts.Off{}))