1	import Base
2	import ../json.bend as Json
3	import ../json/quote.bend as Quote
4	import ./ylex.bend as L
5	
6	# The YAML emitter: block style, two spaces per level, `- ` items under their
7	# key. A string is written plain only when no reader could take it for
8	# another type (L.plain_ok); otherwise it is double-quoted with JSON escapes
9	# (valid YAML). No trailing newline. Pure.
10	
11	# Where a value sits: the document, after `key:`, after `- `, or inside a
12	# chain of fields or items.
13	type Ctx is Data:
14	  CTop{}
15	  CKey{}
16	  CItem{}
17	  CChain{}
18	
19	def pad(+d: Nat) -> String:
20	  String.repeat(" ", d)
21	
22	def str(+s: String) -> String:
23	  Bool.pick(String, L.plain_ok(s), s, Quote.quote(s, False{}))
24	
25	# Before a scalar: a space after `key:`.
26	def lead(+k: Ctx) -> String:
27	  match k:
28	    case CKey{}:
29	      " "
30	    case _:
31	      ""
32	
33	# The indent of a container's lines.
34	def ind(+k: Ctx, +d: Nat) -> Nat:
35	  match k:
36	    case CTop{}:
37	      d
38	    case _:
39	      Nat.add(d, 2n)
40	
41	# Before a container's first line: under a key it starts a new line.
42	def pre(+k: Ctx, +d: Nat) -> String:
43	  match k:
44	    case CKey{}:
45	      "\n" ++ pad(Nat.add(d, 2n))
46	    case _:
47	      ""
48	
49	def is_nil(j: Json.Json) -> Bool:
50	  match j:
51	    case Json.JNil{}:
52	      True{}
53	    case _:
54	      False{}
55	
56	def cont(empty: Bool, +k: Ctx, +d: Nat, lit: String, body: String) -> String:
57	  match empty:
58	    case True{}:
59	      lead(k) ++ lit
60	    case False{}:
61	      pre(k, d) ++ body
62	
63	# A new line for the next field or item, none at the end of the chain.
64	def sep(t: Json.Json, +d: Nat, rest: String) -> String:
65	  match t:
66	    case Json.JNil{}:
67	      ""
68	    case _:
69	      "\n" ++ pad(d) ++ rest
70	
71	# `j` at the base indent `d` in context `k`. Chains (fields, items) carry their
72	# lines at `d`; the first line of a chain starts wherever the caller left off.
73	def y(j: Json.Json, +k: Ctx, +d: Nat) -> String:
74	  match j:
75	    case Json.JNull{}:
76	      lead(k) ++ "null"
77	    case Json.JBool{b}:
78	      lead(k) ++ Json.bool.show(b)
79	    case Json.JNum{t}:
80	      lead(k) ++ t
81	    case Json.JStr{s}:
82	      lead(k) ++ str(s)
83	    case Json.JArr{+items}:
84	      cont(is_nil(items), k, d, "[]", y(items, CChain{}, ind(k, d)))
85	    case Json.JObj{+fields}:
86	      cont(is_nil(fields), k, d, "{}", y(fields, CChain{}, ind(k, d)))
87	    case Json.JNil{}:
88	      ""
89	    case Json.JCons{h, +t}:
90	      "- " ++ y(h, CItem{}, d) ++ sep(t, d, y(t, CChain{}, d))
91	    case Json.JField{key, v, +t}:
92	      str(key) ++ ":" ++ y(v, CKey{}, d) ++ sep(t, d, y(t, CChain{}, d))
93	
94	# One YAML document for the value (no `---`, no trailing newline).
95	def emit(j: Json.Json) -> String:
96	  y(j, CTop{}, 0n)