Initial JS runtime and Arborix Implementation

ext/js/test/reduce.test.js

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+import { strictEqual, ok } from "node:assert";
+import { describe, it } from "node:test";
+import { apply, isLeaf, isStem, isFork } from "../src/tree.js";
+import { reduce } from "../src/cli.js";
+
+describe("tree — basic types", () => {
+  it("Leaf is empty array", () => {
+    ok(isLeaf([]));
+    ok(!isStem([]));
+    ok(!isFork([]));
+  });
+
+  it("Stem is single-element array", () => {
+    ok(isStem([[]]));
+    ok(!isLeaf([[]]));
+  });
+
+  it("Fork is two-element array", () => {
+    ok(isFork([[], []]));
+    ok(!isLeaf([[], []]));
+  });
+});
+
+describe("tree — apply rules", () => {
+  // Leaf = [], Stem = [child], Fork = [right, left]
+
+  it("apply(Leaf, b) = Stem(b)", () => {
+    const b = []; // Leaf
+    const result = apply([], b);
+    ok(isStem(result), "Stem(b) should be a Stem");
+    strictEqual(result[0], b);
+  });
+
+  it("apply(Stem(a), b) = Fork(a, b)", () => {
+    const a = []; // Leaf
+    const b = []; // Leaf
+    const result = apply([a], b);
+    ok(isFork(result), "Fork(a, b) should be a Fork");
+    // Fork = [right, left] = [b, a]
+    strictEqual(result[0], b);
+    strictEqual(result[1], a);
+  });
+
+  it("apply(Fork(Leaf, a), _) = a", () => {
+    // Fork(Leaf, a) = [a, Leaf]
+    const a = []; // Leaf
+    const result = apply([a, []], []);
+    strictEqual(result, a);
+    ok(isLeaf(result));
+  });
+});
+
+describe("tree — reduction", () => {
+  it("reduces Leaf to Leaf", () => {
+    const result = reduce([], 100);
+    ok(isLeaf(result));
+  });
+
+  it("reduces Stem Leaf to Stem Leaf", () => {
+    const result = reduce([[]], 100);
+    ok(isStem(result));
+    ok(isLeaf(result[0]));
+  });
+
+  it("reduces Fork Leaf Leaf to Fork Leaf Leaf", () => {
+    const result = reduce([[], []], 100);
+    ok(isFork(result));
+    ok(isLeaf(result[0]));
+    ok(isLeaf(result[1]));
+  });
+
+  it("S combinator applied to Leaf reduces", () => {
+    // S = t (t (t t)) t = Fork (Fork (Fork Leaf Leaf) Leaf) Leaf
+    // In array form: [[[], []], [], []]
+    const s = [[], [[[], []], []]];
+    const leaf = [];
+    const result = reduce([s, leaf], 100);
+    ok(Array.isArray(result), "S Leaf should reduce to an array");
+  });
+});