1	# src/rules/calls: what the recursion rules (pick, strict, tail, concat,
2	# index) share. A file's defs, each with its name, its signature and its body;
3	# a call's arguments; whether a def calls itself; its parameters, and the type
4	# of the one it walks; and whether it is exempt (a law or a proof never runs,
5	# and a def with no type fills a law: it is a proof).
6	import Base
7	import ../paths.bend as Paths
8	import ../syntax/lex.bend as Lex
9	import ../syntax/tree.bend as Tree
10	import ../syntax/bind.bend as Bind
11	import ../lazy/lazy.bend as Lazy
12	
13	# a def: its name, its own tokens (the signature) and the statements under it
14	type Def is Data:
15	  Def{name: String, sig: Tree.Node, body: Tree.Node}
16	
17	# a def with a name joins the others; one without (half-written) does not
18	def defs.push(mm: Maybe<&2, String>, sig: Tree.Node, body: Tree.Node, acc: List<&2, Def>) -> List<&2, Def>:
19	  match mm:
20	    case None{}:
21	      acc
22	    case Some{name}:
23	      Def{name, sig, body} <> acc
24	
25	# the defs of a parsed source, in order
26	def defs(root: Tree.Node) -> List<&2, Def>:
27	  match root:
28	    case Tree.NCons{Tree.Stmt{Tree.SDef{}, +kids, body}, rest}:
29	      defs.push(Bind.declared(kids), kids, body, defs(rest))
30	    case Tree.NCons{h, rest}:
31	      defs(rest)
32	    case other:
33	      Nil{}
34	
35	# a leaf's kind, none for anything else: kind tests read this, never a text
36	def leaf.kind(nn: Tree.Node) -> Maybe<&2, Lex.TokKind>:
37	  match nn:
38	    case Tree.Leaf{Lex.Tok{k, t, l, c}}:
39	      Some{k}
40	    case other:
41	      None{}
42	
43	# a kind test on a kind, when there is one
44	def kind.of(~test: Lex.TokKind -> Bool, mm: Maybe<&2, Lex.TokKind>) -> Bool:
45	  match mm:
46	    case None{}:
47	      False{}
48	    case Some{k}:
49	      test(k)
50	
51	# a leaf of this kind?
52	def kind.leaf(~test: Lex.TokKind -> Bool, nn: Tree.Node) -> Bool:
53	  kind.of(~test, leaf.kind(nn))
54	
55	# a `:`
56	def kind.colon(kk: Lex.TokKind) -> Bool:
57	  match kk:
58	    case Lex.TColon{}:
59	      True{}
60	    case other:
61	      False{}
62	
63	# a capitalized name
64	def kind.upper(kk: Lex.TokKind) -> Bool:
65	  match kk:
66	    case Lex.TUpper{}:
67	      True{}
68	    case other:
69	      False{}
70	
71	# `->`
72	def kind.arrow(kk: Lex.TokKind) -> Bool:
73	  match kk:
74	    case Lex.TArrow{}:
75	      True{}
76	    case other:
77	      False{}
78	
79	# a plain operator (`-`, `~`, `+`)
80	def kind.oper(kk: Lex.TokKind) -> Bool:
81	  match kk:
82	    case Lex.TOp{}:
83	      True{}
84	    case other:
85	      False{}
86	
87	# a leaf's text, "" for anything else
88	def leaf.text(nn: Tree.Node) -> String:
89	  match nn:
90	    case Tree.Leaf{Lex.Tok{k, t, l, c}}:
91	      t
92	    case other:
93	      ""
94	
95	# the arguments of a group, split at its top-level commas (each a chain)
96	def args.go(kids: Tree.Node, +cur: Tree.Node, +acc: List<&2, Tree.Node>) -> List<&2, Tree.Node>:
97	  match kids:
98	    case Tree.NCons{+h, +rest}:
99	      Lazy.either(List<&2, Tree.Node>, kind.leaf(~Lex.is_comma, h),
100	        _u => args.go(rest, Tree.NNil{}, Tree.reverse(cur, Tree.NNil{}) <> acc),
101	        _v => args.go(rest, Tree.NCons{h, cur}, acc))
102	    case other:
103	      List.reverse(&2, Tree.Node, Tree.reverse(cur, Tree.NNil{}) <> acc)
104	
105	# the arguments of a group
106	def args(kids: Tree.Node) -> List<&2, Tree.Node>:
107	  args.go(kids, Tree.NNil{}, [])
108	
109	# the nth argument, or nothing
110	def arg(as: List<&2, Tree.Node>, nn: Nat) -> Tree.Node:
111	  match as nn:
112	    case Con{h, t} 0n:
113	      h
114	    case Con{h, t} 1n+p:
115	      arg(t, p)
116	    case Nil{} m:
117	      Tree.NNil{}
118	
119	# is there a call of the name, `name(..)`, anywhere under the node?
120	def calls(nn: Tree.Node, +name: String) -> Bool:
121	  match nn:
122	    case Tree.NCons{Tree.Leaf{Lex.Tok{k, +t, l, c}}, Tree.NCons{Tree.Group{Lex.Tok{_, +o, _, _}, kids, _}, rest}}:
123	      +a = calls(kids, name)
124	      +b = calls(rest, name)
125	      Bool.or(Bool.and(String.eq(o, "("), String.eq(t, name)), Bool.or(a, b))
126	    case Tree.Group{open, kids, close}:
127	      calls(kids, name)
128	    case Tree.Stmt{kind, kids, body}:
129	      +a = calls(kids, name)
130	      +b = calls(body, name)
131	      Bool.or(a, b)
132	    case Tree.NCons{h, t}:
133	      +a = calls(h, name)
134	      +b = calls(t, name)
135	      Bool.or(a, b)
136	    case other:
137	      False{}
138	
139	# the kids of a signature's first `(` group: the parameters
140	def params.of(sig: Tree.Node) -> Tree.Node:
141	  match sig:
142	    case Tree.NCons{Tree.Group{Lex.Tok{k, +o, l, c}, +kids, close}, rest}:
143	      +more = params.of(rest)
144	      Bool.pick(Tree.Node, String.eq(o, "("), kids, more)
145	    case Tree.NCons{h, rest}:
146	      params.of(rest)
147	    case other:
148	      Tree.NNil{}
149	
150	# a def's parameters, each its chain up to a comma (`+xs: List<&2, U32>`)
151	def params(sig: Tree.Node) -> List<&2, Tree.Node>:
152	  args(params.of(sig))
153	
154	# a parameter's name: its first lowercase name before the colon ("" for a
155	# type parameter like `-A: Type`)
156	def param_name(pp: Tree.Node) -> String:
157	  match pp:
158	    case Tree.NCons{Tree.Leaf{Lex.Tok{Lex.TName{}, t, l, c}}, rest}:
159	      t
160	    case Tree.NCons{Tree.Leaf{Lex.Tok{Lex.TColon{}, t, l, c}}, rest}:
161	      ""
162	    case Tree.NCons{h, rest}:
163	      param_name(rest)
164	    case other:
165	      ""
166	
167	def names.go(ps: List<&2, Tree.Node>, acc: List<&2, String>) -> List<&2, String>:
168	  match ps:
169	    case Nil{}:
170	      List.reverse(&2, String, acc)
171	    case Con{p, rest}:
172	      names.go(rest, param_name(p) <> acc)
173	
174	# the names of a def's parameters
175	def names(sig: Tree.Node) -> List<&2, String>:
176	  names.go(params(sig), [])
177	
178	# does a chain hold a top-level colon?
179	def has_colon(pp: Tree.Node) -> Bool:
180	  match pp:
181	    case Tree.NCons{h, rest}:
182	      Lazy.or_else(kind.leaf(~kind.colon, h), _u => has_colon(rest))
183	    case other:
184	      False{}
185	
186	# does the chain open with a `-` or `~` operator?
187	def is_live.sign(pp: Tree.Node) -> Bool:
188	  match pp:
189	    case Tree.NCons{+h, rest}:
190	      +t = leaf.text(h)
191	      Bool.and(kind.leaf(~kind.oper, h), Bool.or(String.eq(t, "-"), String.eq(t, "~")))
192	    case other:
193	      False{}
194	
195	# a live parameter: typed, and neither erased (`-A: Type`) nor a template
196	# (`~f: A -> B`); a bare quantity name (`a` in `List.get(a, ..)`) is not one
197	def is_live(+pp: Tree.Node) -> Bool:
198	  Bool.and(Bool.not(is_live.sign(pp)), has_colon(pp))
199	
200	# the head of a parameter's type: the first capitalized name after the colon
201	# (`List` in `+xs: +List<A>`), "" for none
202	def type_head(pp: Tree.Node, +after: Bool) -> String:
203	  match pp:
204	    case Tree.NCons{+h, rest}:
205	      +more = type_head(rest, Bool.or(after, kind.leaf(~kind.colon, h)))
206	      Bool.pick(String, Bool.and(after, kind.leaf(~kind.upper, h)), leaf.text(h), more)
207	    case other:
208	      ""
209	
210	def walked.go(ps: List<&2, Tree.Node>, found: Maybe<&2, String>) -> String:
211	  match ps found:
212	    case Con{+p, rest} None{}:
213	      walked.go(rest, Lazy.stop(Maybe<&2, String>, Bool.not(is_live(p)), None{},
214	        _u => Some{type_head(p, False{})}))
215	    case Con{p, rest} Some{t}:
216	      t
217	    case Nil{} Some{t}:
218	      t
219	    case Nil{} None{}:
220	      ""
221	
222	# the type head of the first live parameter: the one a self-call must shrink
223	def walked(sig: Tree.Node) -> String:
224	  walked.go(params(sig), None{})
225	
226	# does the def walk a list or a string (its first live parameter's type)?
227	def seq(sig: Tree.Node) -> Bool:
228	  +h = walked(sig)
229	  Bool.or(String.eq(h, "List"), String.eq(h, "String"))
230	
231	# a `{` group after the arrow, or a proof further on
232	def returns_proof.or(+brace: Bool, more: Bool) -> Bool:
233	  Bool.or(brace, more)
234	
235	# does the signature return a proof, `-> {a == b : T}`?
236	def returns_proof(sig: Tree.Node) -> Bool:
237	  match sig:
238	    case Tree.NCons{h, +rest}:
239	      match rest:
240	        case Tree.NCons{+g, r2}:
241	          Lazy.either(Bool, kind.leaf(~kind.arrow, h), _u => returns_proof.or(Tree.opens(g, "{"), returns_proof(r2)),
242	            _v => returns_proof(rest))
243	        case _r:
244	          returns_proof(rest)
245	    case other:
246	      False{}
247	
248	# does a chain hold a top-level `->`?
249	def has_arrow(pp: Tree.Node) -> Bool:
250	  match pp:
251	    case Tree.NCons{h, rest}:
252	      Lazy.or_else(kind.leaf(~kind.arrow, h), _u => has_arrow(rest))
253	    case other:
254	      False{}
255	
256	# does the signature write a type: a `:` among its parameters, or a `->`?
257	def typed(+sig: Tree.Node) -> Bool:
258	  Lazy.or_else(has_colon(params.of(sig)), _u => has_arrow(sig))
259	
260	# is the def a proof? One that returns a proof (`-> {a == b : T}`), or one
261	# written with no type at all (`def f(x, y):`), which is how Bend fills the
262	# law named f
263	def proof(+sig: Tree.Node) -> Bool:
264	  Bool.or(returns_proof(sig), Bool.not(typed(sig)))
265	
266	# a law file, a proof file, or a def that is a proof: none of it runs, so its
267	# cost does not matter
268	def exempt(+path: String, sig: Tree.Node) -> Bool:
269	  Bool.or(Paths.is_law_file(path), proof(sig))