1	import Base
2	import ./lex.bend as Lex
3	
4	def tk.kind(t: Lex.Tok) -> U32:
5	  match t:
6	    case Lex.TLBrace{}:
7	      11
8	    case Lex.TLBrack{}:
9	      12
10	    case Lex.TRBrace{}:
11	      21
12	    case Lex.TRBrack{}:
13	      22
14	    case Lex.TComma{}:
15	      3
16	    case _:
17	      0
18	
19	def depth.next(+k: U32, +d: U32) -> U32:
20	  Lex.sel(U32.is_eq(k, 11) || U32.is_eq(k, 12), (d + 1 : U32),
21	    Lex.sel(U32.is_eq(k, 21) || U32.is_eq(k, 22), Lex.sel(U32.is_eq(d, 0), 0, (d - 1 : U32)), d))
22	
23	def stopper(+k: U32, +d: U32) -> Bool:
24	  U32.is_eq(d, 0) && (U32.is_eq(k, 3) || U32.is_eq(k, 21) || U32.is_eq(k, 22))
25	
26	def scan.pick(stop: Bool, rest: Nat) -> Nat:
27	  match stop:
28	    case True{}:
29	      0n
30	    case False{}:
31	      rest
32	
33	# Tokens before the first comma or closer at depth 0.
34	def scan(toks: List<&2, Lex.Tok>, +d: U32) -> Nat:
35	  match toks:
36	    case Nil{}:
37	      0n
38	    case Con{+h, t}:
39	      scan.pick(stopper(tk.kind(h), d), 1n+scan(t, depth.next(tk.kind(h), d)))
40	
41	def last.kind(m: Maybe<&2, Lex.Tok>) -> U32:
42	  match m:
43	    case None{}:
44	      0
45	    case Some{t}:
46	      tk.kind(t)
47	
48	# Is the last token of t the closer `k`?
49	def closed_by(+t: List<&2, Lex.Tok>, k: U32) -> Bool:
50	  U32.is_eq(last.kind(List.last(&2, Lex.Tok, t)), k)
51	
52	def err.of(toks: List<&2, Lex.Tok>) -> String:
53	  match toks:
54	    case Nil{}:
55	      ""
56	    case Con{Lex.TErr{m}, t}:
57	      m
58	    case Con{h, t}:
59	      err.of(t)