1	# src/syntax/word: the name under a (line, col), both 0-based. A name is letters,
2	# digits, `_` and `.` (dots are just characters in a Bend name, and a module
3	# alias rides in front: `Frame.decode`). A position right after a name counts
4	# as on it, as editors put the cursor there.
5	import Base
6	import ../lazy/lazy.bend as Lazy
7	import ../rchars.bend as Rchars
8	
9	# i: the column of the next char; start: where the current run began; run: the
10	# current name, reversed; hit: the name found
11	type W is Data:
12	  W{i: U32, start: U32, run: List<&2, Char>, hit: Maybe<&2, String>}
13	
14	# a char a name may hold: letters, digits, `_` and `.`
15	def is_name(+cc: Char) -> Bool:
16	  Bool.or(Bool.or(Char.is_alpha(cc), Char.is_digit(cc)), Bool.or(Char.is_eq(cc, '_'), Char.is_eq(cc, '.')))
17	
18	# the run's chars (reversed) as a string
19	def text(run: List<&2, Char>) -> String:
20	  Rchars.text(run)
21	
22	# the run holds the column: keep it; otherwise the hit so far
23	def close.yes(ok: Bool, run: List<&2, Char>, hit: Maybe<&2, String>) -> Maybe<&2, String>:
24	  match ok:
25	    case True{}:
26	      Some{text(run)}
27	    case False{}:
28	      hit
29	
30	# an empty run leaves the hit; otherwise the run if start <= col <= i
31	def close.run(run: List<&2, Char>, +start: U32, +ii: U32, +col: U32, hit: Maybe<&2, String>) -> Maybe<&2, String>:
32	  match run:
33	    case Nil{}:
34	      hit
35	    case h <> t:
36	      close.yes(Bool.and(U32.is_le(start, col), U32.is_le(col, ii)), h <> t, hit)
37	
38	# a run that ends at column i holds col when start <= col <= i, unless one already did
39	def close(+ii: U32, +start: U32, run: List<&2, Char>, hit: Maybe<&2, String>, +col: U32) -> Maybe<&2, String>:
40	  match hit:
41	    case Some{s}:
42	      Some{s}
43	    case None{}:
44	      close.run(run, start, ii, col, None{})
45	
46	# a name char joins the run; any other char ends it
47	def step.on(name: Bool, cc: Char, +ii: U32, +start: U32, run: List<&2, Char>, hit: Maybe<&2, String>, +col: U32) -> W:
48	  match name:
49	    case True{}:
50	      W{(ii + 1 : U32), start, cc <> run, hit}
51	    case False{}:
52	      W{(ii + 1 : U32), (ii + 1 : U32), [], close(ii, start, run, hit, col)}
53	
54	# one char: it extends the run of name chars, or ends it (a run holding the
55	# column is the answer)
56	def step(+cc: Char, st: W, +col: U32) -> W:
57	  W{i, start, run, hit} = st
58	  step.on(is_name(cc), cc, i, start, run, hit, col)
59	
60	# the run that held the column, else ""
61	def finish(st: W, col: U32) -> String:
62	  W{i, start, run, hit} = st
63	  Maybe.default(&2, String, close(i, start, run, hit, col), "")
64	
65	# lines still to skip after this char; a newline counts as one
66	def at.skip.n(nl: Bool, nn: U32) -> U32:
67	  match nl:
68	    case True{}:
69	      (nn - 1 : U32)
70	    case False{}:
71	      nn
72	
73	# the next char starts the wanted line when this one was its preceding newline
74	def at.skip.done(nl: Bool, nn: U32) -> Bool:
75	  match nl:
76	    case True{}:
77	      U32.is_eq(nn, 1)
78	    case False{}:
79	      False{}
80	
81	# the source with `n` lines skipped. `done` means this string is the line
82	def at.skip(ss: String, +nn: U32, done: Bool) -> String:
83	  match ss done:
84	    case SNil{} _:
85	      SNil{}
86	    case SCon{h, t} True{}:
87	      SCon{h, t}
88	    case SCon{+h, t} False{}:
89	      at.skip(t, at.skip.n(Char.is_eq(h, '\n'), nn), at.skip.done(Char.is_eq(h, '\n'), nn))
90	
91	# a newline ends the line; any other char is part of it
92	def at.advance(nl: Bool, hh: Char, st: W, +col: U32) -> W:
93	  match nl:
94	    case True{}:
95	      st
96	    case False{}:
97	      step(hh, st, col)
98	
99	# the name at col, from here up to the next newline
100	def at.read(ss: String, stop: Bool, st: W, +col: U32) -> String:
101	  match ss stop:
102	    case SNil{} _:
103	      finish(st, col)
104	    case SCon{h, t} True{}:
105	      finish(st, col)
106	    case SCon{+h, t} False{}:
107	      at.read(t, Char.is_eq(h, '\n'), at.advance(Char.is_eq(h, '\n'), h, st, col), col)
108	
109	# the name under a (line, col) of a source, "" when none
110	def at(source: String, +line: U32, col: U32) -> String:
111	  at.read(at.skip(source, line, U32.is_eq(line, 0)), False{}, W{0, 0, [], None{}}, col)
112	
113	# `Alias.rest` cut at its first dot: ("Alias", "rest"); no dot: (name, "")
114	def cut.go(cs: List<&2, Char>, acc: List<&2, Char>) -> String & String:
115	  match cs:
116	    case Nil{}:
117	      (text(acc), "")
118	    case Con{'.', t}:
119	      (text(acc), String.from_list(t))
120	    case Con{c, t}:
121	      cut.go(t, c <> acc)
122	
123	# `Alias.rest` cut at its first dot: ("Alias", "rest"); no dot: (name, "")
124	def cut(name: String) -> String & String:
125	  cut.go(String.to_list(name), [])
126	
127	# a pair's first
128	def fst(pp: String & String) -> String:
129	  (h, r) = pp
130	  h
131	
132	# a pair's second
133	def snd(pp: String & String) -> String:
134	  (h, r) = pp
135	  r
136	
137	# the part before the first dot
138	def head(name: String) -> String:
139	  fst(cut(name))
140	
141	# the part after the first dot, "" when there is none
142	def rest(name: String) -> String:
143	  snd(cut(name))
144	
145	# the leading run of name chars
146	def run_of(cs: List<&2, Char>) -> List<&2, Char>:
147	  match cs:
148	    case Nil{}:
149	      Nil{}
150	    case Con{+c, t}:
151	      Lazy.stop(List<&2, Char>, Bool.not(is_name(c)), Nil{}, _u => c <> run_of(t))
152	
153	# the name that ends at (line, col): what is being typed, for completion
154	def before(source: String, line: U32, col: U32) -> String:
155	  text(run_of(List.reverse(&2, Char, String.to_list(String.take(
156	    Maybe.default(&2, String, List.get(&2, String, String.lines(source), U32.to_nat(line)), ""),
157	    U32.to_nat(col))))))