1	import Base
2	import ../ByteMemTable.bend as ByteMemTable
3	
4	# Owns the unread suffix of one ordered byte-entry source.
5	type Cursor is Type:
6	  CursorReady{entries: List<&1, ByteMemTable.Entry>}
7	  CursorEnded{}
8	  CursorClosed{}
9	  CursorFailed{code: U32, message: String}
10	
11	# Returns one entry, terminal end, or terminal cursor error.
12	type Step is Type:
13	  CursorItem{entry: ByteMemTable.Entry, cursor: Cursor}
14	  CursorEnd{cursor: Cursor}
15	  CursorError{cursor: Cursor}
16	
17	# Creates a cursor over an already ordered bounded source.
18	def open(entries: List<&1, ByteMemTable.Entry>) -> Cursor:
19	  CursorReady{entries}
20	
21	# Returns at most one entry and retains the remaining source suffix.
22	def next(cursor: Cursor) -> Step:
23	  match cursor:
24	    case CursorReady{entries}:
25	      match entries:
26	        case Nil{}: CursorEnd{CursorEnded{}}
27	        case Con{entry, tail}: CursorItem{entry, CursorReady{tail}}
28	    case CursorEnded{}: CursorEnd{CursorEnded{}}
29	    case CursorClosed{}: CursorEnd{CursorClosed{}}
30	    case CursorFailed{code, message}:
31	      CursorError{CursorFailed{code, message}}
32	
33	# Closes an active cursor while preserving terminal outcomes.
34	def close(cursor: Cursor) -> Cursor:
35	  match cursor:
36	    case CursorReady{_}: CursorClosed{}
37	    case CursorEnded{}: CursorEnded{}
38	    case CursorClosed{}: CursorClosed{}
39	    case CursorFailed{code, message}: CursorFailed{code, message}