1	# Pipes to a started program, and this program's stdin, as Files of UTF-8 lines.
2	# A POLYFILL: Bend has no pipes to a started program, no way to kill one, and no stdin handle yet.
3	# Delete this module when Base has them, and call Base instead.
4	# A line has at most max bytes with its LF or CRLF: a longer one fails with E2BIG (7).
5	import Base
6	
7	# Code
8	# ====
9	
10	# This program's stdin. A File owns its descriptor: ask for it once.
11	def stdin() -> IO(File):
12	  import "./std.c"
13	  import "./std.js"
14	
15	# Start a program, with its stdin and stdout as pipes: its process id, the File that writes its
16	# stdin, and the File that reads its stdout. Its stderr is ours. Closing the stdin File gives it
17	# EOF; nothing waits for it to exit. On JS, it runs on Bun on Linux and macOS only; elsewhere it
18	# fails with ENOSYS.
19	def open(
20	  program: String,
21	  args: List<String>
22	) -> IO(Result<&1, &1, U32 & String, U32 & (File & File)>):
23	  import "./open.c"
24	  import "./open.js"
25	
26	# Kills the program that open started with pid, unless it has ended: then it fails with ESRCH (3).
27	# It never kills a program that open did not start, though the system gives an ended program's pid
28	# to another one.
29	def kill(pid: U32) -> IO(Result<&1, &1, U32 & String, Unit>):
30	  import "./open.c"
31	  import "./open.js"
32	
33	# A line with no LF that ends the input is the last line; one that does not is too long.
34	def read_line.peeked(
35	  next: File & Result<&1, &1, U32 & String, String>,
36	  text: String
37	) -> File
38	  & Result<&1, &1, U32 & String, Maybe<String>>:
39	  match next:
40	    case (file, Fail{error}):
41	      (file, Fail{error})
42	    case (file, Done{SNil{}}):
43	      (file, Done{Some{text}})
44	    case (file, Done{SCon{_, _}}):
45	      (file, Fail{(7, "a line is longer than its cap")})
46	
47	# The line of a piece that ends with its LF: the piece without the LF, and the CR before it, if any.
48	def read_line.unended(+piece: String) -> String:
49	  +line = String.take(piece, Nat.sub(String.length(piece), 1n))
50	  Bool.pick(
51	    String,
52	    String.ends_with(line, "\r"),
53	    String.take(line, Nat.sub(String.length(line), 1n)),
54	    line
55	  )
56	
57	def read_line.if(
58	  file: File,
59	  ended: Bool,
60	  piece: String
61	) -> IO(File & Result<&1, &1, U32 & String, Maybe<String>>):
62	  match ended:
63	    case True{}:
64	      IO.pure(
65	        File & Result<&1, &1, U32 & String, Maybe<String>>,
66	        (file, Done{Some{read_line.unended(piece)}})
67	      )
68	    case False{}:
69	      do IO<File & Result<&1, &1, U32 & String, Maybe<String>>>:
70	        next: File & Result<&1, &1, U32 & String, String> <- File.read_line(file, 1)
71	        return read_line.peeked(next, piece)
72	
73	def read_line.got(
74	  got: File & Result<&1, &1, U32 & String, String>
75	) -> IO(File & Result<&1, &1, U32 & String, Maybe<String>>):
76	  match got:
77	    case (file, Fail{error}):
78	      IO.pure(File & Result<&1, &1, U32 & String, Maybe<String>>, (file, Fail{error}))
79	    case (file, Done{SNil{}}):
80	      IO.pure(File & Result<&1, &1, U32 & String, Maybe<String>>, (file, Done{None{}}))
81	    case (file, Done{SCon{h, t}}):
82	      +piece: String = SCon{h, t}
83	      read_line.if(file, String.ends_with(piece, "\n"), piece)
84	
85	# The next line of file, as it comes, without its LF or CRLF; None at the end of the file.
86	def read_line(file: File, max: U32) -> IO(File & Result<&1, &1, U32 & String, Maybe<String>>):
87	  IO.bind(
88	    File & Result<&1, &1, U32 & String, String>,
89	    File & Result<&1, &1, U32 & String, Maybe<String>>,
90	    File.read_line(file, max),
91	    read_line.got
92	  )
93	
94	def write_lines.text(lines: List<String>) -> String:
95	  match lines:
96	    case Nil{}:
97	      ""
98	    case Con{line, rest}:
99	      line ++ "\n" ++ write_lines.text(rest)
100	
101	# Writes each line to file, with its LF.
102	def write_lines(file: File, lines: List<String>) -> IO(File & Result<&1, &1, U32 & String, Unit>):
103	  File.write(file, write_lines.text(lines))