1	# Pure generators: each takes a Rand.Rng and returns a value beside the next state.
2	import Base
3	import bend-kit-random@0.1.0.1/random.bend as Rand
4	import bend-kit-bytes@0.3.2.0/bytes.bend as Bytes
5	
6	# A generator is `Rand.Rng -> T & Rand.Rng`. The same seed replays the same value:
7	#   (xs, r) = Gen.list(~U32, ~Gen.u32, 8, Rand.seed(42))
8	# Sizes are capped at 1024 so lengths and Nats stay small enough to build and shrink.
9	
10	# n, capped at 1024.
11	def cap(+n: U32) -> U32:
12	  U32.min(n, 1024)
13	
14	# A uniform U32.
15	def u32(r: Rand.Rng) -> U32 & Rand.Rng:
16	  Rand.next(r)
17	
18	# A uniform U32 in [lo, hi); lo when hi <= lo + 1.
19	def u32.range(+lo: U32, hi: U32, r: Rand.Rng) -> U32 & Rand.Rng:
20	  Rand.range(lo, hi, r)
21	
22	# A uniform size in [0, min(max, 1024)].
23	def size(+max: U32, r: Rand.Rng) -> U32 & Rand.Rng:
24	  Rand.below((cap(max) + 1 : U32), r)
25	
26	def nat.fin(xr: U32 & Rand.Rng) -> Nat & Rand.Rng:
27	  (x, r) = xr
28	  (U32.to_nat(x), r)
29	
30	# A uniform Nat in [0, min(max, 1024)].
31	def nat(+max: U32, r: Rand.Rng) -> Nat & Rand.Rng:
32	  nat.fin(size(max, r))
33	
34	def char.fin(xr: U32 & Rand.Rng) -> Char & Rand.Rng:
35	  (x, r) = xr
36	  (Chr{x}, r)
37	
38	# A printable ASCII char, ' ' (32) through '~' (126).
39	def char(r: Rand.Rng) -> Char & Rand.Rng:
40	  char.fin(Rand.range(32, 127, r))
41	
42	# n + 1 chars prepended to acc; cr holds the next char.
43	def string.go(n: Nat, acc: String, cr: Char & Rand.Rng) -> String & Rand.Rng:
44	  match n:
45	    case 0n:
46	      (c, r) = cr
47	      (SCon{c, acc}, r)
48	    case 1n+p:
49	      (c, r) = cr
50	      string.go(p, SCon{c, acc}, char(r))
51	
52	# Exactly n printable ASCII chars.
53	def string.of(n: Nat, r: Rand.Rng) -> String & Rand.Rng:
54	  match n:
55	    case 0n:
56	      (SNil{}, r)
57	    case 1n+p:
58	      string.go(p, SNil{}, char(r))
59	
60	def string.fin(nr: Nat & Rand.Rng) -> String & Rand.Rng:
61	  (n, r) = nr
62	  string.of(n, r)
63	
64	# Printable ASCII of length in [0, min(max, 1024)].
65	def string(+max: U32, r: Rand.Rng) -> String & Rand.Rng:
66	  string.fin(nat(max, r))
67	
68	# Byte i and the n bytes after it; xr holds byte i (Bytes.set keeps its low 8 bits).
69	def bytes.go(n: Nat, b: Bytes.Bytes, +i: U32, xr: U32 & Rand.Rng) -> Bytes.Bytes & Rand.Rng:
70	  match n:
71	    case 0n:
72	      (x, r) = xr
73	      (Bytes.set(b, i, x), r)
74	    case 1n+p:
75	      (x, r) = xr
76	      bytes.go(p, Bytes.set(b, i, x), (i + 1 : U32), Rand.next(r))
77	
78	def bytes.start(n: Nat, +len: U32, r: Rand.Rng) -> Bytes.Bytes & Rand.Rng:
79	  match n:
80	    case 0n:
81	      (Bytes.new(0), r)
82	    case 1n+p:
83	      bytes.go(p, Bytes.new(len), 0, Rand.next(r))
84	
85	# Exactly min(len, 1024) uniform octets, one draw each.
86	def bytes.of(+len: U32, r: Rand.Rng) -> Bytes.Bytes & Rand.Rng:
87	  +n = cap(len)
88	  bytes.start(U32.to_nat(n), n, r)
89	
90	def bytes.fin(nr: U32 & Rand.Rng) -> Bytes.Bytes & Rand.Rng:
91	  (n, r) = nr
92	  bytes.of(n, r)
93	
94	# Uniform octets, length in [0, min(max, 1024)].
95	def bytes(+max: U32, r: Rand.Rng) -> Bytes.Bytes & Rand.Rng:
96	  bytes.fin(size(max, r))
97	
98	# n + 1 items prepended to acc; hr holds the next item.
99	def list.go(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, n: Nat, acc: List<&2, T>, hr: T & Rand.Rng) -> List<&2, T> & Rand.Rng:
100	  match n:
101	    case 0n:
102	      (h, r) = hr
103	      (h <> acc, r)
104	    case 1n+p:
105	      (h, r) = hr
106	      list.go(~T, ~gen, p, h <> acc, gen(r))
107	
108	# Exactly n items from gen. The first draw ends up last; replay is unaffected.
109	def list.of(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, n: Nat, r: Rand.Rng) -> List<&2, T> & Rand.Rng:
110	  match n:
111	    case 0n:
112	      (Nil{}, r)
113	    case 1n+p:
114	      list.go(~T, ~gen, p, Nil{}, gen(r))
115	
116	def list.fin(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, nr: Nat & Rand.Rng) -> List<&2, T> & Rand.Rng:
117	  (n, r) = nr
118	  list.of(~T, ~gen, n, r)
119	
120	# Items from gen, length in [0, min(max, 1024)].
121	def list(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, +max: U32, r: Rand.Rng) -> List<&2, T> & Rand.Rng:
122	  list.fin(~T, ~gen, nat(max, r))
123	
124	def maybe.some(~T: Data, hr: T & Rand.Rng) -> Maybe<&2, T> & Rand.Rng:
125	  (h, r) = hr
126	  (Some{h}, r)
127	
128	def maybe.if(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, none: Bool, r: Rand.Rng) -> Maybe<&2, T> & Rand.Rng:
129	  match none:
130	    case True{}:
131	      (None{}, r)
132	    case False{}:
133	      maybe.some(~T, gen(r))
134	
135	def maybe.pick(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, xr: U32 & Rand.Rng) -> Maybe<&2, T> & Rand.Rng:
136	  (+x, r) = xr
137	  maybe.if(~T, ~gen, U32.is_eq(x, 0), r)
138	
139	# None one time in four, else Some from gen.
140	def maybe(~T: Data, ~gen: Rand.Rng -> T & Rand.Rng, r: Rand.Rng) -> Maybe<&2, T> & Rand.Rng:
141	  maybe.pick(~T, ~gen, Rand.below(4, r))
142	
143	def map.fin(~A: Type, ~B: Type, ~f: A -> B, ar: A & Rand.Rng) -> B & Rand.Rng:
144	  (a, r) = ar
145	  (f(a), r)
146	
147	# gen's value through f.
148	def map(~A: Type, ~B: Type, ~f: A -> B, ~gen: Rand.Rng -> A & Rand.Rng, r: Rand.Rng) -> B & Rand.Rng:
149	  map.fin(~A, ~B, ~f, gen(r))
150	
151	def bind.fin(~A: Type, ~B: Type, ~k: A -> Rand.Rng -> B & Rand.Rng, ar: A & Rand.Rng) -> B & Rand.Rng:
152	  (a, r) = ar
153	  k(a, r)
154	
155	# gen's value picks the next generator: bind(~Nat, ~List<&2, U32>, ~(r => Gen.nat(8, r)), ~(n => r => Gen.list.of(~U32, ~Gen.u32, n, r)), r).
156	def bind(~A: Type, ~B: Type, ~gen: Rand.Rng -> A & Rand.Rng, ~k: A -> Rand.Rng -> B & Rand.Rng, r: Rand.Rng) -> B & Rand.Rng:
157	  bind.fin(~A, ~B, ~k, gen(r))
158	
159	def pair.snd(~A: Type, ~B: Type, a: A, br: B & Rand.Rng) -> (A & B) & Rand.Rng:
160	  (b, r) = br
161	  ((a, b), r)
162	
163	def pair.fst(~A: Type, ~B: Type, ~gb: Rand.Rng -> B & Rand.Rng, ar: A & Rand.Rng) -> (A & B) & Rand.Rng:
164	  (a, r) = ar
165	  pair.snd(~A, ~B, a, gb(r))
166	
167	# ga's value then gb's, drawn in that order.
168	def pair(~A: Type, ~B: Type, ~ga: Rand.Rng -> A & Rand.Rng, ~gb: Rand.Rng -> B & Rand.Rng, r: Rand.Rng) -> (A & B) & Rand.Rng:
169	  pair.fst(~A, ~B, ~gb, ga(r))