From 8bcaac40ee1afb8c36f98beabe0348ae3713d44d Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud.bailly@iohk.io>
Date: Sat, 25 Jan 2025 18:31:41 +0100
Subject: Generate a random list

---
 pbt/ts/src/index.ts    | 40 ++++++++++++++++++++++++-------------
 pbt/ts/src/property.ts | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+), 14 deletions(-)
 create mode 100644 pbt/ts/src/property.ts

(limited to 'pbt/ts/src')

diff --git a/pbt/ts/src/index.ts b/pbt/ts/src/index.ts
index 3a71ccf..46454f0 100644
--- a/pbt/ts/src/index.ts
+++ b/pbt/ts/src/index.ts
@@ -1,20 +1,32 @@
-type Result = 'OK' | 'Falsified' | 'Exception';
+import "dotenv/config";
+import Prando from 'prando';
+import { Gen } from "./property";
 
-type TestResult<A> = {
-  result: Result,
-  seed: number,
-  counterexample: A | null
-};
+let genint: Gen<number> = (rng: Prando) =>
+  (size: number) =>
+  rng.nextInt(-size, size);
 
-type Predicate<A> = (a: A) => boolean;
 
-type Gen<A> = (s: number) => (() => A);
+function genlist<A>(gen: Gen<A>): Gen<A[]> {
+  return (rng: Prando) => {
+    let g = gen(rng);
+    return (size: number) => {
+      let result = [];
+      for (let i = 0; i < size; i++) {
+        result.push(g(size));
+      }
+      return result;
+    };
+  };
+}
 
-type Shrinker<A> = (a: A) => [A];
+function generate<A>(gen: Gen<A>): A {
+  let rng = new Prando(Math.random() * 1000);
+  return gen(rng)(100);
+}
 
-function property<A>(seed: number,
-  predicate: Predicate<A>,
-  generator: Gen<A>,
-  shrinker: Shrinker<A>): TestResult<A> {
-  return {result: 'OK', seed, counterexample: null};
+async function main() {
+  console.log('list: ' + generate(genlist(genint)));
 }
+
+main();
diff --git a/pbt/ts/src/property.ts b/pbt/ts/src/property.ts
new file mode 100644
index 0000000..e8d3a21
--- /dev/null
+++ b/pbt/ts/src/property.ts
@@ -0,0 +1,53 @@
+import Prando from "prando";
+
+type Result = 'OK' | 'Falsified' | 'Exception';
+
+type ShrinkResult<A> = { counterexample: A, shrinks: number };
+
+type TestResult<A> = {
+  result: Result,
+  counterexample: ShrinkResult<A> | null
+};
+
+type Predicate<A> = (a: A) => boolean;
+
+export type Gen<A> = (rng: Prando) => ((size: number) => A);
+
+type Shrinker<A> = (a: A) => [A];
+
+const MAX_SUCCESS = 100;
+
+function findMinimalCounterExample<A>(x: A,
+  predicate: Predicate<A>,
+  shrinker: Shrinker<A>,
+  depth: number = 0): ShrinkResult<A> {
+  let xs = shrinker(x);
+  let counterexample = x;
+  let shrinks = depth;
+  for (let y of xs) {
+    if (!predicate(y)) {
+      let shrink = findMinimalCounterExample(y, predicate, shrinker, depth + 1);
+      if (shrink.shrinks > depth) {
+        counterexample = shrink.counterexample;
+        shrinks = shrink.shrinks;
+      }
+    }
+  }
+  return { counterexample, shrinks };
+}
+
+export function property<A>(rng: Prando,
+  size: number,
+  predicate: Predicate<A>,
+  generator: Gen<A>,
+  shrinker: Shrinker<A>): TestResult<A> {
+  let gen = generator(rng);
+  for (let i = 0; i < MAX_SUCCESS; i++) {
+    let x = gen(size);
+    if (!predicate(x)) {
+      let counterexample = findMinimalCounterExample(x, predicate, shrinker);
+      return { result: 'Falsified', counterexample };
+    }
+  }
+  return { result: 'OK', counterexample: null };
+}
-- 
cgit v1.2.3