1	# rule param: a parameter name shorter than 2 characters. A single uppercase
2	# letter is a type parameter (`A`, `T`), and a bare parameter or one typed
3	# `Quant` is a quantity. Locals, pattern binders and a law's `for` names are
4	# not parameters. A PROOF.bend's parameters are the names the law bound.
5	import Base
6	import ../../paths.bend as Paths
7	import ../../role.bend as Role
8	import ../../src.bend as Src
9	import ../../finding.bend as F
10	import ../../syntax/bind.bend as Bind
11	import ../../lazy/lazy.bend as Lazy
12	import ../tokens.bend as T
13	
14	# one character, and a capital: a type parameter
15	def check.letter(cs: List<&2, Char>) -> Bool:
16	  match cs:
17	    case Con{c, Nil{}}:
18	      Char.is_upper(c)
19	    case other:
20	      False{}
21	
22	# `A`, `T`, `H`
23	def check.upper(+nm: String) -> Bool:
24	  check.letter(String.to_list(nm))
25	
26	# no type, or `: Quant`: a quantity parameter (`a` in `List<a, A>`). The
27	# note is read with its string literals cut to their quote: a `:` inside a
28	# string is no type
29	def check.quant(+note: String) -> Bool:
30	  +cn = T.code(note)
31	  Bool.or(Bool.not(String.contains(cn, ":")), String.ends_with(cn, ": Quant"))
32	
33	# shorter than 2
34	def check.short(+nm: String) -> Bool:
35	  Nat.is_lt(String.length(nm), 2n)
36	
37	# a parameter, not a local or a pattern
38	def check.is_param(kk: Bind.BindKind) -> Bool:
39	  match kk:
40	    case Bind.KParam{}:
41	      True{}
42	    case other:
43	      False{}
44	
45	# a type parameter or a quantity, which are allowed to be one letter
46	def check.allowed(+nm: String, +note: String) -> Bool:
47	  Bool.or(check.upper(nm), check.quant(note))
48	
49	def check.go(binds: List<&2, Bind.Bind>, +path: String) -> List<&2, F.Finding>:
50	  match binds:
51	    case Nil{}:
52	      Nil{}
53	    case Con{Bind.Bind{+nm, +line, +col, +kind, +note}, rest}:
54	      +more = check.go(rest, path)
55	      +hit = Bool.and(check.is_param(kind), Bool.and(check.short(nm), Bool.not(check.allowed(nm, note))))
56	      Bool.pick(List<&2, F.Finding>, hit,
57	        F.Finding{path, line, col, U32.from_nat(String.length(nm)), "param",
58	          "Parameter " ++ nm ++ " is too short; use at least 2 characters."} <> more, more)
59	
60	def check.on(binds: List<&2, Bind.Bind>, +path: String) -> List<&2, F.Finding>:
61	  Lazy.stop(List<&2, F.Finding>, Paths.is_proof(path), [], _u => check.go(binds, path))
62	
63	# the rule; a proof's parameters stay the law's names
64	def check(ss: Src.Src) -> List<&2, F.Finding>:
65	  Src.Src{path, text, toks, tree, bound, items} = ss
66	  Bind.Bound{binds, uses, scopes} = bound
67	  check.on(binds, path)
68	
69	# the rule, told the file's role (src/role.bend): a proof file is skipped
70	def check.role(rr: Role.Role, ss: Src.Src) -> List<&2, F.Finding>:
71	  Src.Src{path, text, toks, tree, bound, items} = ss
72	  Bind.Bound{binds, uses, scopes} = bound
73	  Lazy.stop(List<&2, F.Finding>, Role.is_proof(rr), [], _u => check.go(binds, path))