From 21af3dca203deadcb72eeb88c686ddb8d7a6448b Mon Sep 17 00:00:00 2001
From: Troels Henriksen <athas@sigkill.dk>
Date: Fri, 29 May 2026 12:51:03 +0200
Subject: [PATCH] Type-indexed random value generation.

The purpose of this PR is to introduce a combinator-based module for generating
random values of compound types.
---
 lib/github.com/diku-dk/cpprandom/gen.fut | 99 ++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 lib/github.com/diku-dk/cpprandom/gen.fut

diff --git a/lib/github.com/diku-dk/cpprandom/gen.fut b/lib/github.com/diku-dk/cpprandom/gen.fut
new file mode 100644
index 0000000..bfe17cd
--- /dev/null
+++ b/lib/github.com/diku-dk/cpprandom/gen.fut
@@ -0,0 +1,99 @@
+-- | Random value generation.
+
+import "random"
+
+module type gen = {
+  -- | A generator for values of type t.
+  type^ gen 't
+
+  -- | An RNG state used for generating values.
+  type rng
+
+  -- | Generate a random value from a generator.
+  val generate 't : rng -> gen t -> (rng, t)
+
+  -- | Apply function to result of generator.
+  val fmap 'a 'b : (a -> b) -> gen a -> gen b
+
+  val i8 : gen i8
+  val i16 : gen i16
+  val i32 : gen i32
+  val i64 : gen i64
+
+  val u8 : gen u8
+  val u16 : gen u16
+  val u32 : gen u32
+  val u64 : gen u64
+
+  -- | Generates numbers in range (-1,1).
+  val f16 : gen f16
+
+  -- | Generates numbers in range (-1,1).
+  val f32 : gen f32
+
+  -- | Generates numbers in range (-1,1).
+  val f64 : gen f64
+
+  val pair 'a 'b : gen a -> gen b -> gen (a, b)
+  val arr 'a : (n: i64) -> gen a -> gen ([n]a)
+}
+
+module mk_gen (E: rng_engine) : gen with rng = E.rng = {
+  type rng = E.rng
+  type^ gen 't = E.rng -> (E.rng, t)
+
+  def generate rng gen = gen rng
+
+  def fmap f gen rng =
+    let (rng, x) = gen rng
+    in (rng, f x)
+
+  module i8_dist = uniform_int_distribution i8 E
+  module i16_dist = uniform_int_distribution i16 E
+  module i32_dist = uniform_int_distribution i32 E
+  module i64_dist = uniform_int_distribution i64 E
+
+  module u8_dist = uniform_int_distribution u8 E
+  module u16_dist = uniform_int_distribution u16 E
+  module u32_dist = uniform_int_distribution u32 E
+  module u64_dist = uniform_int_distribution u64 E
+
+  module f16_dist = uniform_real_distribution f16 E
+  module f32_dist = uniform_real_distribution f32 E
+  module f64_dist = uniform_real_distribution f64 E
+
+  def i8 = i8_dist.rand (i8.lowest, i8.highest)
+  def i16 = i16_dist.rand (i16.lowest, i16.highest)
+  def i32 = i32_dist.rand (i32.lowest, i32.highest)
+  def i64 = i64_dist.rand (i64.lowest, i64.highest)
+
+  def u8 = u8_dist.rand (u8.lowest, u8.highest)
+  def u16 = u16_dist.rand (u16.lowest, u16.highest)
+  def u32 = u32_dist.rand (u32.lowest, u32.highest)
+  def u64 = u64_dist.rand (u64.lowest, u64.highest)
+
+  def f16 = f16_dist.rand (-1, 1)
+  def f32 = f32_dist.rand (-1, 1)
+  def f64 = f64_dist.rand (-1, 1)
+
+  def pair f g rng =
+    let (rng, x) = f rng
+    let (rng, y) = g rng
+    in (rng, (x, y))
+
+  def arr n f rng =
+    E.split_rng n rng
+    |> map f
+    |> unzip
+    |> \(rngs, xs) -> (E.join_rng rngs, xs)
+}
+
+module RNG = xorshift128plus
+module G = mk_gen RNG
+
+def random_matrix (size: i64) : [][]f64 =
+  let rng = RNG.rng_from_seed [i32.i64 size, 1, 2, 3]
+  let size = G.fmap (\x -> 1 + (i64.abs x) % size) G.i64
+  let (rng, (n, m)) = G.generate rng (G.pair size size)
+  let (_, M) = G.generate rng (G.arr (n * m) G.f64)
+  in unflatten M