1	# The pieces the scanner hands the parser, and the errors both report.
2	
3	import Base
4	
5	# A place in the text: the line and column (each from 0, a column counted in
6	# characters) and the character's index from the start.
7	type Mark is Data:
8	  Mark{line: Nat, col: Nat, idx: Nat}
9	
10	# How a scalar was written.
11	type Style is Data:
12	  Plain{}
13	  Single{}
14	  Double{}
15	  Literal{}
16	  Folded{}
17	
18	# A token, as libyaml names them. A scanner error ends the tokens with Broken.
19	type Tok is Data:
20	  StreamStart{}
21	  StreamEnd{}
22	  VersionDir{major: Nat, minor: Nat}
23	  TagDir{handle: String, prefix: String}
24	  DocStart{}
25	  DocEnd{}
26	  BSeqStart{}
27	  BMapStart{}
28	  BEnd{}
29	  FSeqStart{}
30	  FSeqEnd{}
31	  FMapStart{}
32	  FMapEnd{}
33	  BEntry{}
34	  FEntry{}
35	  KeyTok{}
36	  ValueTok{}
37	  AliasTok{name: String}
38	  AnchorTok{name: String}
39	  TagTok{handle: String, suffix: String}
40	  ScalarTok{text: String, style: Style}
41	  Broken{error: Error}
42	
43	type Token is Data:
44	  Token{tok: Tok, start: Mark, end: Mark}
45	
46	# Why a text didn't load: it isn't YAML, or it is but the schema can't
47	# load it (a bad !!int, an unknown alias, a repeated key).
48	type Cause is Data:
49	  Syntax{}
50	  Content{}
51	
52	# What went wrong, where, and why. A syntax error reads as a problem and
53	# what was being read: "did not find expected key while parsing a block
54	# mapping".
55	type Error is Data:
56	  Error{why: String, at: Mark, cause: Cause}
57	
58	def mark.line(m: Mark) -> Nat:
59	  match m:
60	    case Mark{line, col, idx}:
61	      line
62	
63	def mark.col(m: Mark) -> Nat:
64	  match m:
65	    case Mark{line, col, idx}:
66	      col
67	
68	def mark.idx(m: Mark) -> Nat:
69	  match m:
70	    case Mark{line, col, idx}:
71	      idx
72	
73	# "at line 2 column 5", counting from 1.
74	def mark.show(m: Mark) -> String:
75	  match m:
76	    case Mark{line, col, idx}:
77	      "line " ++ Nat.show(1n+line) ++ " column " ++ Nat.show(1n+col)
78	
79	# The error as one line: "mapping values are not allowed in this context at
80	# line 1 column 5".
81	def error.show(e: Error) -> String:
82	  match e:
83	    case Error{why, at, cause}:
84	      why ++ " at " ++ mark.show(at)
85	
86	def error.why(e: Error) -> String:
87	  match e:
88	    case Error{why, at, cause}:
89	      why
90	
91	def error.at(e: Error) -> Mark:
92	  match e:
93	    case Error{why, at, cause}:
94	      at