1	# files: an effect service: a file's text by path, where Base lives, and
2	# the working directory a relative path is read against.
3	import Base
4	
5	# effect service: a file's text, where Base is, and the working directory
6	type Files is Type:
7	  Files{read: String -> IO(Maybe<&2, String>), base_path: Unit -> IO(String), cwd: Unit -> IO(String)}
8	
9	# None when the file cannot be read
10	def read(ff: Files, path: String) -> IO(Maybe<&2, String>):
11	  Files{r, _b, _c} = ff
12	  r(path)
13	
14	# the path of Base, from a files service
15	def base_path(ff: Files) -> IO(String):
16	  Files{_r, b, _c} = ff
17	  b(Unit{})
18	
19	# the working directory, from the root; "" when it cannot be named
20	def cwd(ff: Files) -> IO(String):  # noqa: L001 effect accessor
21	  Files{_r, _b, c} = ff
22	  c(Unit{})
23	
24	# every path read, in order (a missing file is a None)
25	def read_all(~ff: Files, paths: List<&2, String>) -> IO(List<&2, Maybe<&2, String>>):  # noqa: L001 effect accessor
26	  match paths:
27	    case Nil{}:
28	      IO.pure(List<&2, Maybe<&2, String>>, [])
29	    case Con{p, rest}:
30	      do IO<List<&2, Maybe<&2, String>>>:
31	        r : Maybe<&2, String> <- read(ff, p)
32	        more : List<&2, Maybe<&2, String>> <- read_all(~ff, rest)
33	        return r <> more