1	# lsp/path: just enough path arithmetic to follow a relative import.
2	import Base
3	
4	# a segment lands on the stack (reversed): `..` pops, `.` and `` do nothing
5	def push(+seg: String, +acc: List<&2, String>) -> List<&2, String>:
6	  Bool.pick(List<&2, String>, String.eq(seg, ".."), List.tail(&2, String, acc),
7	    Bool.pick(List<&2, String>, Bool.or(String.eq(seg, "."), String.is_empty(seg)), acc, seg <> acc))
8	
9	# every segment pushed, in order
10	def norm(segs: List<&2, String>, acc: List<&2, String>) -> List<&2, String>:
11	  match segs:
12	    case Nil{}:
13	      acc
14	    case Con{s, t}:
15	      norm(t, push(s, acc))
16	
17	# dir and rel as one absolute path, its `.` and `..` resolved
18	def join(dir: String, rel: String) -> String:
19	  "/" ++ String.join(List.reverse(&2, String, norm(String.split(dir ++ "/" ++ rel, '/'), [])), "/")
20	
21	# the directory of a file's path
22	def dir(path: String) -> String:
23	  join(path, "..")